Abstract: The present invention relates to a detector device and, more particularly, to a detector device comprising a self-diagnosis means for monitoring the correct performance or otherwise of the device. During testing, the device, which normally operates using the Doppler shift principle, is arranged to influence the phase and/or amplitude of the received signal in response to an applied test signal. The received signal may be a Doppler shifted version of a transmitted signal. Combining the phase and/or amplitude shifted version of the received signal and the signal from the local oscillator produces an IF signal that is indicative of the phase and/or amplitude shift. If the device is operating correctly, that signal should have a predetermined range of characteristics. If the self-diagnosis means determines that the produced signal falls outside of the predetermined range of characteristics, an alarm is raised to alert, for example, maintenance personnel to the problem.

Abstract: An intrusion detector having a transmitter, receiver, detector, signal processor, and control unit is disclosed. The transmitter is able to transmit waves into a defined space and has a variable output power. The receiver is able to receive those waves after reflection. The detector is connected to the receiver and able to detect a signal based on a change in the waves after reflection, where the detected signal is representative of any motion in the defined space. The signal processor is able to process the detected signal in order to determine if an intrusion has occurred. The control unit is able to determine any change in the detected signal, and to increase the output power of the transmitter in response to such change. A method for performing such intrusion detection is also disclosed.

Abstract: A pool alarm system for alerting when an object such as a child has entered a pool filled with water. The pool alarm system includes, a sensor assembly for detecting when an object has entered the water in a pool. The sensor assembly includes a housing that is mountable on a side wall of the pool. A first sensor is mounted on the housing for detecting movement of the surface of the water. In one embodiment of the present invention, the first sensor is designed to detect surface movement of the water in the pool caused by an object entering and disturbing the surface of the water. A warning assembly is provided for warning an individual in a vicinity of the pool that the sensor has been activated. The warning assembly preferably includes a speaker that is mounted on the housing for emitting sound to audibly warn an individual in a vicinity of the pool that the sensor has been activated.

Abstract: There is provided a device in which surroundings of a building can be monitored using a sensor; when detecting an intruder, an object can be detected even in the case of bad weather; and a predetermined area can be monitored using as few sensors as possible. The device includes a security system which emits a radio wave from a building to a predetermined area outside the building to detect an object, and on the basis of output of the object detecting unit, a judgment is made as to whether or not the object will intrude into the predetermined area.

Abstract: A detection system for detecting intruders moving in the vicinity of a defined path comprises a distributed antenna, for example an open transmission line, extending along the path, and an array of discrete antennas extending alongside the distributed antenna and within a predetermined distance therefrom. The discrete antennas and the distributed antenna define a plurality of detection zones. A radio frequency transmitter is connected to each of the discrete antennas, and a complementary receiver in a control unit at a remote location is connected to the distributed antenna. The control unit also controls the transmitters, and the array of antennas to exchange radio frequency energy between the distributed antenna and the discrete antennas and analyzes the energy received from the discrete antennas so as to detect perturbations caused by an intruder moving adjacent said path and adjacent a particular antenna.

Abstract: A FM CW cable guided radar for the detection and location of outdoor perimeter intruders. Helically wound outer conductors on coaxial transmit and receive transmission lines provide a slow wave structure to support the propagation of external electromagnetic fields. The two leaky coaxial lines are enclosed in an extruded plastic jacket with the outer conductors in continuous electrical contact along the length of the cable. A chirp frequency modulation provides a continuous target response having a baseband frequency that is proportional to the distance along the length of the cable. After location determination, the amplitude of the response is compared to a location specific threshold to determine if an intruder is present.

Abstract: A Wide Area Metal Detection (WAMD) system and method for security screening a crowd of people is provided. The system comprises at least one Magnetic Field Generator (MFG), e.g., a Horizontal Magnetic Field Generator (HMFG) buried below a walking surface for generating a magnetic field, a plurality of magnetic field sensors located within the sensing area of the MFG for sensing a metallic object, based on eddy currents in the magnetic field, and a location indicator for indicating a location of an individual with the metallic object at a position corresponding to that of one of the plurality of magnetic field sensor that sensed the metallic object. At least one video camera is included for identifying the individual at the location indicated by the location indicator and tracking further movements of the individual.

Abstract: An electronic label reading system is disclosed having an interrogator including a transmitter for generating an interrogation signal and a receiver for detecting and decoding a reply signal. The system also has an interrogation field creation means including a transmitter antenna connected to the transmitter for generating from the interrogation signal an interrogation electromagnetic field through which objects possessing code responding labels may pass. The code responding labels include label receiving antennas for receiving from the interrogation field a label interrogation signal, means for generating label reply signals, and means for generating from the label reply signals, reply electromagnetic fields. The system also has a receiver antenna connected to the receiver for receiving the reply signals from the label reply fields.

Abstract: To provide an immersion object detection system capable of detecting an immersion object within a detection target area and specifying a position thereof irrespective of a short distance/long distance. A millimeter wave is irradiated to a detection area from a millimeter-wave RF unit through an antenna unit, and the reflected wave is detected. In the case that an immersion object exists in a short-distance area from a radar unit, the directly reflected waves from the immersion object is analyzed, thereby specifying the position of the immersion object, and in the case that the immersion object exists in a long-distance area from the radar unit, the position of the immersion object is specified in accordance with the position of the reflection member which cannot detect among the group of reflection members placed within the detection area.

Abstract: A security sensor 1 having a disturbance detecting capability capable of detecting the presence of an obstacle purposefully applied to the sensor 1 in an attempt to fool or tamper the sensor 1 includes a carrier body A having an infrared sensor element 4, an incident side enclosure 5 mounted on the carrier body A, a light projecting element 11 for projecting a disturbance detecting beam L1, a light receiving element 12 for receiving disturbance detecting beam L1, first and second light guide members 8, 9 operatively associated with the light projecting element 11 and the light receiving element 12, respectively, said first and second light guide members 8, 9 being cooperative with each other to define an optical path L along and adjacent an outer surface of the incident side enclosure 5 or an outer surface of the carrier body A adjacent the incident side enclosure 5, a detecting circuit 15 for detecting a presence or absence of an obstacle, applied to at least one of the first and second light guide members 8

Abstract: The invention relates to a proximity or presence switch arrangement operating in accordance with the inductive principle, comprising at least one inductor integrated in an oscillating circuit and an electronic control and evaluation device connected downstream for sensing or detecting the approach and/or presence of a material influencing electromagnetic fields.

Abstract: An apparatus (10) and method for detecting an intrusion into a predetermined area. The apparatus (10) includes a transmitter (28) and a receiver (30). The receiver (30) generates an output signal indicative of reflected return signals received. The apparatus (10) also includes a controller (38). The controller (38) receives the output signal from the receiver (30) and determines a peak value of the output signal during a first time window. The first time window continues no longer than a first maximum duration when the peak value of the output signal during the first maximum duration is at least a predetermined value. The first time window continues no longer than a second maximum duration when the peak value of the output signal during the first maximum duration is less than the predetermined value.

Abstract: The present invention provides a security system that can provide a user with data on the directional movement, velocity and location of an object within and around the perimeter of a structure with the use of radio energy. The system comprises a sensor unit having at least one antenna for transmission of a signal into a defined area of the structure. Any intrusion in the area is detected upon a change in the waveform received by the antenna. A received signal is transmitted from the sensor unit to a control unit, comprising, in part, a preprogrammed data processing unit that can determine the movement of the intruder. Utilization of a plurality of sensor units allows the user to obtain additional information on the velocity and location of the intruder. Additionally, as with conventional security systems, the system can provide an electrical signal to activate a sound and/or light device to attract the attention of the intruder and warn others of the intruder's presence.

Abstract: A wave-discriminating inductive electronic device includes a special integrated circuit that is inducible by a proximity feeble electromagnetic signal generated by a general mobile phone during receiving and transmitting signals, so that the induced integrated circuit is able to control and drive another integrated circuit that includes voice and motor driving circuits. Voices and vibrations produced by the integrated circuit enable the wave-discriminating inductive electronic device to provide a highly interesting entertaining effect.

Abstract: A warning system comprises a piezo-electric ceramic capable of resonating with an ultrasonic wave having a frequency within a predetermined frequency band and thus outputting an electric signal, a resonator capable of detecting only a signal component having a specific frequency from the electric signal output from the piezoelectric ceramic. When the resonator has detected a signal component having a specific frequency, an alarm signal is continuously generated for a predetermined time set by a timer, so that a warning notice is produced by an alarm device in accordance with the alarm signal.

Abstract: An apparatus (10) and method are provided for detecting an intrusion into a predetermined area. The apparatus (10) includes a transmitter (28) for transmitting a signal within the predetermined area. A first receiver (30) is oriented toward a first location within the predetermined area and receives reflected return signals of the transmitted signal. A second receiver (32) is oriented toward a second location within the predetermined area and receives reflected return signals of the transmitted signal. The second location is different from the first location. A controller (42) determines whether reflected return signals received by the first and the second receivers (30 and 32) indicate an intrusion or a non-intrusion event. The controller (42) provides an alarm signal for an alarm (44) when only one of the reflected return signals received by the first and the second receivers (30 and 32) indicates an intrusion.

Abstract: A frequency detector that detects a frequency signal indicative of the proximity of a transportation vessel or an intrinsically-safe area. The frequency detector may be associated with any type of electronic device. The frequency detector detects the presence of a frequency signal that is emitted by a transportation vessel and/or a frequency beacon associated with the transportation vessel. The frequency detector and/or container may disable, shut down, or reduce power of any electro-magnetic field generating devices associated with the frequency detector and/or container if the frequency detector receives a frequency signal indicative of the inside or proximity of a transportation vessel or an intrinsically-safe area. The container also includes a self-check frequency generator that emits a frequency signal capable of being detected by the frequency detector.

Abstract: Disclosed is a stimuli providing indicator (107) that is responsive to nearby transmitted radio signals. Fixed and mobile stations may produce such signals. In addition a cellular telephone operating at a high transmit power may be detected. Indicator (107) may be supported by a lens (103) which itself may be supported by at least one head mount (101).

Abstract: The vehicle detection system described herein uses wireless magnetic sensors to measure changes in the earth's magnetic field to detect vehicles. The sensors may measure the presence and location of a vehicle, as well as the speed of passing vehicles. The sensor may also be capable of identifying and classifying vehicles. Each sensor and/or sensor system may be configured to consume so little power that it can operate from a battery for up to 10 years. While the preferred embodiment is wireless, the sensor and/or sensor systems may be configured to operate in a wired environment.

Abstract: Telesurveillance installation and process for operating this installation.

Abstract: A vehicle door stop safety system for preventing closure of a vehicle door when an object moves between an open door and body of the vehicle. The system includes field producing means for producing a field adjacent to a latch end of the door, when the door is open; and sensing means for sensing an interruption of the field and for producing a block or stop signal when the interruption is sensed. Blocking means is provided for blocking closure of the door upon an interruption of the field. Alternatively, braking means is provided for stopping the door's movement at a position when an interruption of the field is sensed. Controller means is provided for actuating the blocking or braking means upon sensing by the sensing means of an interruption of the field.

Abstract: A cap is fit to a sensor case having a sensor-mounting hollow portion integrally formed therewith into which an ultrasonic sensor is fit. A plate spring is fit onto an outside of the sensor case to engage the plate spring with the cap. This plate spring integrally holds together both the sensor case and the cap. Having been constructed as above, the invention provides an easy integral assembly of a sensor case and a cap by means of a single plate spring and exhibits the ability for mounting and fixing the detector to a bumper or the like of a vehicle.

Abstract: A security sensor 1 having a disturbance detecting capability capable of detecting the presence of an obstacle 8 purposefully applied to the sensor 1 in an attempt to fool or tamper the sensor 1 includes a carrier body A having an infrared sensor element 4, an incident side enclosure 5, such as a lens defining a detection area B, mounted on the carrier body A, a light projecting element 11 for projecting a disturbance detecting beam L1 from inside of the incident side enclosure 5 towards the incident side enclosure 5, a light receiving element 12 for receiving the disturbance detecting beam L1 reflected from the incident side enclosure 5, and a detecting circuit 15 for detecting a presence or absence of the obstacle 8 on the incident side enclosure 5, based on an amount of light received by the light receiving element 12.

Abstract: An apparatus for the detection of any intruder passing through an electronic fence is disclosed. The electronic fence is formed by a millimeter wave radar positioned at one end of the fence and a plurality of reflectors placed along the floor of the fence as well as on a structure at its far end. The fence is formed of a plurality of electromagnetic beams traversing between the radar antenna or antennas and each of the reflectors. A sufficient number of beams inhabit the fence volume to make traversing the fence by an intruder without detection essentially impossible. The radar reflection from the intruder's person is used to report the location of an intruder attempting to traverse the electronic fence near the radar end and is the secondary means of detection at greater ranges where breaking of one or more electromagnetic beams constitutes the primary means of detection.

Abstract: An apparatus (10) and a method for detecting an intrusion into an area (e.g., 14) are provided. The apparatus (10) has a transmitter (30) for transmitting a signal within the area. The apparatus (10) also has a receiver (32) for receiving reflected return signals of the transmitted signal and for generating an output signal indicative of the reflected return signals received. The apparatus (10) also includes a controller (36) for analyzing the output signal. The controller includes a processor (43) for running an algorithm that simulates performance of a capacitor, which charges and discharges in response to an output signal, by increasing a virtual capacitor value when the output signal is greater than a threshold and by decreasing the virtual capacitor value when the output signal is less than the threshold.

Abstract: An ultrasonic monitoring method and system is disclosed. The method includes transmitting a sequence of ultrasonic pulses into a space; receiving a resultant echo signal; monitoring the space for intrusion by comparing the resultant echo signal received in a first window period with the resultant echo signal received in a second window period, wherein the pulses within the sequence are separated by a time interval such that echoes generated from the pulses are superimposed to form the resultant signal.

Abstract: A control device controls undesirable emissions from devices in an environment by transmitting signals to devices in the environment. The signals can be either control signals that require the devices in the environment to operate at a reduced functionality, or warning signals indicating an acceptable level of functionality for the devices. The levels of functionality for the devices are chosen to correspond to desired emission levels by the devices in the environment. The control device utilizes a transmitting device to transmit the signals to devices in the environment, and can include sensors to detect conditions within the environment. Another embodiment of the invention uses a control device as a relay for communication signals between devices within the environment and signal sources outside of the environment.

Abstract: An intrusion detection system and method are provided that can utilize impulse radio technology to detect when an intruder has entered a protection zone. In addition, the intrusion detection system and method can utilize impulse radio technology to determine a location of the intruder within the protection zone and also track the movement of the intruder within the protection zone. Moreover, the intrusion detection system and method can utilize impulse radio technology to create a specially shaped protection zone before trying to detect when and where the intruder has penetrated and moved within the protection zone.

Abstract: A demodulator of an evaluating unit for a device for detecting objects derives a useful signal from a supplied input signal with the aid of a carrier signal. The demodulator further derives a test signal with the aid of a modulated carrier signal. An evaluator detects as a function of the useful signal whether an object is being detected and, as a function of the test signal the functionality of the device.

Abstract: In a detection system for detecting intruders in the vicinity of a predetermined path or line defined by a distributed antenna, for example an open transmission line, an array of discrete antennas are provided alongside the distributed antenna and within a predetermined distance therefrom. The antennas are spaced apart from each other and the distributed antenna and define a plurality of detection zones. A radio frequency transmitter is connected to one of the distributed antenna and the array of discrete antennas, and a complementary receiver is connected to the other of the distributed antenna and the array of discrete antennas. A control unit controls the transmitter, receiver and array of antennas to exchange radio frequency energy several times via the distributed antenna and selected ones of the array of antennas and to detect perturbations caused by an intruder moving adjacent the path and adjacent a particular antenna.

Abstract: A security structure intended particularly for the construction of security containers and security rooms. The security structure has an alarm mat integral therewith. The alarm mat is constructed from one or more insulated, electrically conductive threads, wires or the like, or from one or more light conducting, optical fibres. The thread or threads is/are disposed to form continuous meshes, lopps, or eyes of the kind obtained when knitting or crocheting.

Abstract: Collision avoidance apparatus (28, 30) is mounted on a host vehicle (20) to detect the presence of an adjacent vehicle (22) within a monitored zone (24, 26). A sensor module (30) includes a plurality of discrete sensor systems for monitoring unique portions of the monitored zone (24, 26), each of which comprises an emitter (52) emitting a fixed frequency modulated beam (58) of light energy (54) with a predetermined burst length into its unique portion of the monitored zone (24, 26), and a receiver (68) having a field of view (62), substantially aligned with emitted beam (58) to produce a fixed optical overlap area (A), and for sensing light energy (66) and generating a received signal. A frequency generator (48) produces two or more predetermined different fixed frequencies for use by the emitter (52) to emit beams (58) at each frequency. A phase shifter (70) produces a phase shifted reference signal with a different predetermined phase delay relationship to each fixed frequency.

Abstract: A FM CW cable guided radar for the detection and location of outdoor perimeter intruders. Helically wound outer conductors on coaxial transmit and receive transmission lines provide a slow wave structure to support the propagation of external electromagnetic fields. The two leaky coaxial lines are enclosed in an extruded plastic jacket with the outer conductors in continuous electrical contact along the length of the cable. A chirp frequency modulation provides a continuous target response having a baseband frequency that is proportional to the distance along the length of the cable. After location determination, the amplitude of the response is compared to a location specific threshold to determine if an intruder is present.

Abstract: A motion detector of an alarm system has a microwave sensor and a passive infrared sensor, and includes signal processing logic for initiating an anti-masking evaluation upon detection of certain conditions. The detector then samples the sensor signals and compares the signals to a series of possible outcomes. Some of the possible outcomes represent masking conditions, while others represent normal conditions. A match with masking conditions results in an alarm signal being generated.

Abstract: System for a vehicle, comprising a seat fitted with a measuring device of the electromagnetic field type, an airbag arranged to protect the occupant of the seat in the event of an accident, this airbag having several modes of operation, and an operating device designed to cause the airbag to inflate in the event of an accident, selectively according to one of the modes of operation of this airbag on the basis of a parameter representing the mass of the occupant of the seat, as measured by the electromagnetic field-type measuring device.

Abstract: A sensor panel including a transmit coil for producing a magnetic field in response to a source signal, a plurality of receive elements, each responsive to changes in the magnetic field incident thereon to provide an output, and a cancellation circuit arranged to remove from the outputs any signal induced in each receive element by the transmit coil. The receive elements are arranged in a matrix to provide an indication of the shape of a detected object. The sensor panel can be incorporated as part of a detection apparatus for use in airports and the like, and can also be used to detect buried landmines and ordinances.

Abstract: The invention relates to an intrusion detection process for detecting an intrusion within a space, in which at least two acoustic or electromagnetic signals are emitted at different frequencies (f1, f2, . . . fn) inside said space; at a point inside said space, a signal is received that is the combination of the signals emitted and reflected in said space; the characteristics of the demodulated signals of different frequencies are compared to establish the presence or absence of an intrusion; an intrusion signal is generated when the presence of an intruder is confirmed. The invention also proposes an intrusion detection device implementing the process according to the invention.

Abstract: The invention relates to a motion detector or proximity switch for detecting moving objects, wherein a high frequency electromagnetic radiation is generated by a free running oscillator and transmitted via a transmitter antenna. The transmitter antenna detects the Doppler modified radiation reflected by the moving object as a function of its phase position or amplitude variation. The radiation is compared with the transmitted radiation parameters in an evaluation device with a view to producing an output signal. The inventive detector is characterized in that it included a free running oscillator having a feedback guaranteed by at least one transmitter antenna ANT RX and at least one receiver antenna ANT TX which are oriented towards the object and coupled via a side or leakage radiation.

Abstract: A wearable electric field detector has a housing mountable on a user's person and including a sensing circuit responsive to an electric field to generate a signal which varies in proportion to the strength of the sensed field, and an alarm circuit coupled to the sensing circuit for producing an intermittent audible alarm signal, which has a repetition rate varying in proportion to the strength of the field, and a visible alarm signal. A mute circuit is manually activatable for selectively muting the audible alarm and then automatically reenabling it after a predetermined time period. The detector includes a manually-actuatable test circuit. There is no on-off switch, the detector being disabled by being disposed in a shielded carrying case.

Abstract: An apparatus for detecting an object in a pool of liquid has at least one transmitting transducer for generating one of a sonic, ultrasonic and electromagnetic signal into the pool of liquid from a side of the pool of liquid and such that the signal is conveyed through the entire volume of the pool of liquid; at least one receiving transducer for receiving an echo of the signal transmitted by the transmitting transducer; and a circuit coupled to the transmitting and receiving transducers for providing an electrical signal to the transmitting transducer to generate the signal and for receiving an electrical signal from the receiving transducer indicative of the echo, the circuit including a processor for processing the signal indicative of the echo to determine if an object is present in the pool of liquid.

Abstract: The invention provides apparatus and methods for detecting electromagnetic energy using an array of detectors arranged in at least one row and multiple columns. A single crystal body has multiple doped regions disposed therein. Each one of the detectors produces charge in a corresponding one of the doped regions in the body in response to electromagnetic energy impinging upon that detector. A first charge transfer device includes an output port and multiple serially coupled charge storage cells including multiple first charge transfer regions disposed in the body parallel to the row, or rows, of detectors. Multiple second charge transfer devices include multiple second charge transfer regions disposed in the body transverse to the row, or rows, of detectors and the charge storage cells. Each one of the second charge transfer regions is adapted to transfer charge produced in a corresponding one of the doped regions to a corresponding one of the charge storage cells.

Abstract: A intruder detecting apparatus for detecting a intruder invading an detection area defined in, for example, a window, entrance or apron region in front of one or more wall-mounted paintings includes a first sensor 2X having an detection area 7A defined in the front side of the objects 5 and 6 to be watched and the region upwardly of those objects 5 and 6 to be watched, and a second sensor 2Y having an detection area 7B defined in the front side of the objects 5 and 6 to be watched and the region downwardly of those objects 5 and 6 to be watched. A timer-equipped logic circuit 13 is provided in at least one of the first and second sensors 2X and 2Y. The other of the first and second sensors 2X and 2Y has an output path 17 provided therein for outputting a detection signal a from a detector 10 within such sensor to an external circuit.

Abstract: A brake light system is arranged to respond to movement within an r.f. field to provide a signal used to activate the brake light when movement within the r.f. field exceeds a predetermined velocity.

Abstract: A system for detecting and tracking movement within a building has a plurality of portable microwave detector units for deploying outside the walls of the building. Each detector unit has a microwave module for transmitting microwaves through the building walls into a monitored area and for detecting radiation reflected back to the unit from the monitored area, and an output device for transmitting an alarm signal from the unit if a shift is detected in the reflected radiation frequency, indicating movement within the area. A receiver unit receives alarm signals from the detector units and produces an output signal for each detector unit currently detecting movement to provide the user with information on the location of any movement within the building.

Abstract: The present invention provides a door safety system, which operates safely and surely with respect to an automatic door system having doors moving rapidly, and which prevents a person or an obstacle getting near the doors from colliding with the moving doors. Translucent-type and reflex-type non-contact proximity switches are provided at moving doors for detecting a person or an obstacle and for controlling movements of the doors so as to prevent the person or the obstacle from colliding with the moving doors. Furthermore, a cable guide electrically connects the moving doors and a side of building so that the person or the obstacle can be detected with respect to a moving space of the moving doors.

Abstract: An electromagnetic intrusion detection system which has a transmitter that produces a radio frequency output which is received by an antenna which receives the output and radiates an electromagnetic field into the surrounding space. This in turn responds to the presence of an object or an environmental condition causing absorption and/or reflection. A monitoring apparatus monitors power consumption and thus provides a signal output relating to the environmental condition and/or intrusion.

Abstract: In order to trigger an airbag in a differentiated way, the position of a vehicle occupant is determined in a way that is as immune to interference as possible. This is achieved by a distance measurement in which the seatbelt that is in contact with the vehicle occupant serves as an active reference position. The distance between the seatbelt and known points within the vehicle permits the position of the seatbelt and the vehicle occupant to be determined. The distance measurement is performed using magnetic field transmitter units and receiver units. The transmitter unit is preferably integrated into the belt.

Abstract: A method of locating a concealed conductor is performed by generating a magnetic field with a direction in which the field is a maximum. The magnetic field is rotated until that direction is directed towards the conductor. In this way, a signal is induced in the conductor which has a maximum value when that direction is directed towards the conductor. The induced signal is detected in the conductor, using a detector arranged to determine the direction of the conductor relative to the detector. The detector detects when the induced signal has the maximum value.

Abstract: Apparatus for testing an alarm sensor includes a receiver, means for modifying a signal received by the receiver to simulate a “moving target” return signal, means for varying the power of the modified signal, a transmitter for transmitting the modified signal to the sensor, and means for detecting a signal output by the alarm sensor. The sensor is mounted on an opposite side of an anechoic chamber to the transmitter and the receiver. The apparatus includes a controller to reduce the attenuation of an attenuator, forming part of the power varying means, from a high level until the modified signal received by the alarm sensor is large enough to trigger an output signal.

Abstract: An intrusion detection system for detecting objects entering a particular region is comprised of a transmitter, receiver and cable assembly, wherein the transmitter and receiver are connected at opposite ends of the cable assembly. In a first embodiment, the cable assembly is comprised of a transmit and receive cable pair that are aligned at each end and positioned at a constant distance from each other along the length. The transmitter is connected to the transmit cable at one end of the cable assembly, and the receiver is connected to the receive cable at the opposite end of the assembly, with a uniform electromagnetic field established between the cables. An intrusion perturbs the field, which causes a change in the magnitude and/or phase of the received signal. In a second embodiment, the cable assembly is comprised of a single detection cable with the transmitter and receiver connected to opposite ends.