Abstract: A control device for an alarm system includes a sensor circuit, an amplifier circuit for amplifying a sensor signal from the sensor circuit, a filter circuit for filtering an amplified output of the amplifier circuit, and first and second comparators, each having a reference input and a test input which receives a filtered signal output of the filter circuit. The first reference signal present at the reference input of the first comparator is lower than the second reference signal present at the reference input of the second comparator. The first comparator activates an oscillator circuit to generate an intermittent activating signal when the filtered signal output exceeds the first reference signal. A first alarm signal source presents a first control signal to the alarm system upon reception of the intermittent activating signal from the oscillator circuit.

Abstract: An intrusion warning system for protecting a partition, for example, a wall, ceiling, window, fenced cage, against intrusion by cutting through and/or climbing over. A vibration detector is mounted on the partition and the partition vibration detected by sensing the electric signal generated by the detector. The sensed electric signal is filtered, AM detected, shaped and processed to determine if an intrusion type event has occurred. Since research has determined that the materials composing a partition cause the vibration frequency induced into the detector to vary considerably, the system has a plurality of band filters to allow selection of the band to best monitor the partition for a given application. The system supports this selection with a built in display for the input level through an input amplifier and filters for the frequency band selected. A given stimulus to the detector thus can be analyzed for each band and the band providing the highest output selected.

Abstract: A method of supervising the operation of an intrusion detector having a housing, the method including periodically generating in the housing at least one sound wave signal, sensing an acoustic image formed in the housing in response to the at least one sound wave signal, constructing a sensed signal envelope responsive to the sensed acoustic image, periodically comparing the sensed signal envelope with a reference signal envelope to determine whether a predetermined criterion of similarity between the sensed signal envelope and the reference signal envelope is met and, if the similarity criterion is not met, providing a predetermined, sensible, indication.

Abstract: The detector contains a structure-borne sound microphone connected to an electronic evaluation unit with a piezoelectric sensor (18) for structure-borne sound vibrations. This sensor has a vibrating bar (28), which is attached by means of hybrid technology to a carrier (27). The vibrating bar (28) is formed by a bimorph element and the carrier by an electrically conductive ceramic wafer.

Abstract: A vehicle interior is monitored by storage of sample signals in a memory of a computer and comparison of at least one stored sample signal with a signal picked up on a detector of sound waves from the interior of the vehicle. An identity or similarity test is conducted by the computer and an alarm device is triggered when the predetermined degree of similarity is reached to signal an incursion.

Abstract: A device for controlling power to an electrical load. The device has two components: a portable desktop detector unit and an electrical powerstrip. The desktop detector detects the presence of a human in a room and sends signals to the powerstrip to supply power to or withhold power from individual electrical loads connected to the strip. Since the detector is portable, it can be positioned and repositioned at different locations in a room to maximize its ability to detect the presence of a person. The system can also communicate by wireless signals to a wall-mounted control unit to control light fixtures in the room. When used with a wall-mounted control unit, a photo sensor that detects the level of ambient light in a room allows the system to adjust the brightness of lights in the room depending upon the available ambient light level.

Abstract: A shock detector for measuring intermittent shock events comprises a mechanical delay line to supply delayed output motion in response to input motion along an input axis. A transducer converts the delayed output motion to an electrical signal representative of the delayed output motion. The transducer is generally in a respective inactive state to reduce the power consumption of the shock detector. A relatively low power motion sensor, such as low power accelerometer or tilt actuated switch, is employed for switching the transducer to a respective active state in response to the input motion thereby allowing the shock detector to measure any intermittent shock event regardless of the generally inactive state of the transducer.

Abstract: A self contained, programmable alarm system is securely attached to an article and activates an alarm device when the article is moved. A programmable controller provides the operational routines which determine the function of the alarm system. Non-position-sensitive, vibration activated switching means are included for activating the alarm device after sensing movement of the article. The alarm system can be mounted in a water resistant enclosure that can be locked by a further switch that physically locks the enclosure to the article, electrically connects power to the alarm system, and provides access to a secure compartment within the enclosure for battery storage.

Abstract: A monitoring sensor for articles susceptible to theft, comprising a sensor element for monitoring a proper contact of the sensor with the article and a connecting cable for connecting the sensor to a monitoring circuit of a theft protection system is proposed. During disconnecting of the proper contact with the article, the sensor makes available a measured variable, the alteration in which can be evaluated by the monitoring circuit as an alarm situation. To enable the sensor to be produced in a flat type of construction and also to be easily connected to curved surfaces of an article to be protected, the sensor and the sensor element are of a flexible design, whereby any alteration in shape during disconnecting of the proper contact between sensor and article results in an alteration in the shape of the contact surface element and in an alteration in the measured variable.

Abstract: A batteryless sensor includes either a micro miniature generator/gear train or a piezoelectric crystal to convert a movement of a door or window to an ersatz V.sub.cc transient power supply to radiate a coded RF signal to a receiver, a distance away. The receiver may monitor a multiplicity of sensors to identify a source of an intrusion.

Abstract: A security system for pools and spas incorporates two distinct sections. The first control means allows for automatic operation and consists of sensors that detect and keep track of the number of adults entering or leaving the pool area and deactivate or activate the second control means of the system. Within the second control means, a motion detector first senses movement of an animate object in the area adjacent to the pool, which then interrupts, for a certain period of time, pool cleaning equipment to allow the aquatic sonic transducer to operate at a more effective sensitivity which senses frequencies characteristic of splashing over other sounds, coupled to circuitry responsive to the same frequencies. When splashing is detected, alarms are activated which then need to be reset.

Abstract: Potential harm to an underground utility conveyance (12), resulting from excavation by a backhoe (14) in the vicinity of the conveyance, is sensed by a sensor (32, 40, 42 or 44) that detects a disturbance attributable to the presence of the backhoe. In response to the sensor detecting such a disturbance, a control unit (34) triggers a warning device (36, 38) to generate a warning to alert the backhoe operator of the presence of the underground utility conveyance (12).

Abstract: This invention relates to multi purpose shock sensor being used as a vehicle burglar alarm and/or a security system for restricted area, which consists of a cap, a vibration sensing element, a sealed cavity, and a balance weight in the characterized that having a safety cover securely fixed and surrounded with the elastic cap, preparing a gap having a fixing surface and a free surface on inner peripherals of the safety cover, fixing a lid on the safety cover, forming a groove on a peripherals of a balance weight, forming a coupling hole on the center of the cap, and coupling the balance weight into the coupling hole in the top of the cap.

Abstract: Apparatus and a method for detecting glass breaking from an impact. Low frequencies are detected that are characteristics of the glass flexing from the impact, and high frequencies are detected that are characteristic of a) the sound of the impact and b) the glass breaking. An alarm signal is issued when the low and high frequencies occur in a predetermined sequence, and have appropriate durations, that are characteristic of glass breaking events. More specifically, the alarm sounds only when low frequencies are detected not before the high frequencies are first detected but within a predetermined time period after the first detection of the high frequencies.

Abstract: An acoustic transducer has an output which is fed through a preamplifier to a multiple of parallel filters. Each parallel filter passes a band of signals having frequencies within a predetermined range of frequencies. Each band of signals is converted from analog to digital and input to a signal processing unit. The peak amplitude value and the average value of the output from each parallel filter is determined. The peak amplitude value and average amplitude value are compared to determine if a pretrip condition occurs. If a pretrip condition occurs, the average value is saved and compared with the peak amplitude value for a select number of time periods to determine if a trip condition exists. A special test can be used which alters the number of time periods used in determining if a trip condition exists, based on a comparison the peak amplitude value between two of the bands.

Abstract: A method of indicating the threat level of an incoming shock to an electronically secured vehicle and eliminating spurious signals developed from the interaction of EMF and RF energy fields with the shock sensor including the steps of sensing a shock delivered to the vehicle indicative of an attempted intrusion, generating an electric signal the strength of which is proportional to the intensity of the shock, analyzing the signal to determine if it is of a low, generally non-threatening intensity or a higher, generally security-threatening intensity, ignoring the first 5 milliseconds of the signal produced by the shock sensor, ignoring all signals that do not disappear and later reappear, and producing either a first pulse representing a low intensity signal, or separate first and second pulses representing a signal containing both low intensity and higher intensity components.

Abstract: The invention is a barbed tape barrier that includes a tube that acts as a support for the loops of barbed tape. Located within the tube is a fiber optic cable that is vibration sensitive and connected to a control unit. If an intruder disturbs the barrier, the resultant vibrations will be detected by the control unit and an alarm will be actuated.

Abstract: An automobile anti-theft alarm has an internal air pressure sensor and an external pressure sensor and a connecting electric circuit. The internal pressure sensor is mounted inside the compartment of the automobile and is connected through the electric circuit to an alarm in such a way that when the internal pressure sensor detects a pressure change the alarm will sound. The external pressure sensor is mounted outside the compartment of the automobile. Air pressure fluctuations originating outside the vehicle compartment are transmitted by the flexure of the vehicle body into the vehicle. The electric circuit is connected to an alarm and to both the inner and external pressure sensors in such a way that external air pressure fluctuations affect both sensors and the outer pressure sensor produces a voltage in the electric circuit which prevents the alarm from being activated.

Abstract: A motion detection device for use as a monitor for patient movement, inclng a sensor for generating motion signals, an integrator for integrating the motion signals over a period of time, and a threshold level of signals generating an alarm signal upon exceeding a predetermined minimum value of the motion signals to activate an alarm. The sensor includes an edge detector for providing a motion sensed outpost of a series of sharp voltage rises and falls to generate a sequence of voltage pulses of predetermined magnitude and time duration which generate an alarm signal if the pulses are generated faster than a preset rate of voltage decay based upon a preselected minimum movement to be sensed.

Abstract: The present invention is directed to a local telephone line tamper protection device. In particular, it protects a conventional security alarm system using telephone lines from being disabled by an intruder before it has a chance to function. Telephone service lines are generally accessible from the exterior of the structure. The alarm system is protected by providing an service enclosure having a strong box and a conduit to enclose the telephone service box and service line. The protection device includes sensors and switches to inform the security monitor before an intruder can disable the alarm system. A vibration sensor is activated when movements of the strong box and conduit occur and a signal is generated to announce the intruder. The strong box has two access doors where the locked outside door must be opened to access the locked inside door. Each access door has a separate tamper switch means that generates a signal to also activate the alarm system.

Abstract: A security device, intended for use as a temporary or permanent vehicle security device, having an intrusion detection device in the form of a pair of electrical contacts supported on a shock amplifying, rigid base and responsive to percussive-type forces for generating a detection signal. At least one of the electrical contacts is supported on a relatively stiff cantilevered arm which will not respond to small movements and vibrations, to thereby avoid generating frequent false alarms. Any contact closure signal from the electrical contacts is processed by a detection circuit which counts multiple contact closures and/or measures total closure time, thus ignoring signals generated from small forces or vibrations, thereby preventing against the source of most false alarms when generating a detection signal.

Abstract: An independent alarm system which is carried by a housing member designed to be located adjacent to or within building openings, and at various other site locations, or adjacent to specific to-be-protected objects. The housing member is free standing, for example, swingably suspended from a window frame, ceiling or a separate frame. The housing member has an agitation sensor and a proximity or tilt sensor incorporated therein and electrically wired to a first signal. When the housing member is agitated while in its original position, or when it is moved from its original position to a second position, the agitation sensor and/or the proximity/tilt sensor is activated, which in turn causes the first signal to be actuated. The agitation and proximity/tilt sensors are both battery powered. By being pulsed, the alarm circuit may be always "on", yet be fully operational for a period of thirty six months, and greater using a single set of batteries.

Abstract: A glass break detector system (10) includes a low frequency (LF) detector (28) that is responsive to a pressure wave transducer (12) to detect the amplitude of a low frequency, generally sinusoidal acoustic wave signal resulting from a physical contact with a glass window. The LF detector includes a peak analyzer (42) that compares absolute values of sequential first and second amplitudes (P1, P2) of a low frequency signal derived from the low frequency acoustic wave signal to determine an appropriate alarm response. The LF detector enables the alarm if the absolute value of the first amplitude (P1) is greater than the absolute value of the second amplitude (P2) or if P1 or P2 amplitudes exceed saturation thresholds. The LF detector also includes a slope analyzer (40) that determines whether the low frequency signal exhibits atypical characteristics that generally indicate glass breakage.

Abstract: Sound, vibration and motion are sensed within a motor vehicle to detect glass breakage and unauthorized intrusion into the interior or passenger compartment of the vehicle. Sound and vibration sensing are used to detect glass breakage with motion detection by means of radar or microwaves being utilized for intrusion detection to provide reliable recurring entry detection. The system may be operated to activate the motion sensing only after glass breakage is detected to permit persons and pets to occupy a motor vehicle having a security sensor system which is fully armed. Numerical values are assigned to specific physical sounds and vibrations with the resulting totals being compared to a threshold to determine whether glass breakage has occurred.

Abstract: A shock sensor includes a mass suspended in a flexible support arranged to resonate when subjected to a mechanical shock, a microphone spaced closely to the mass, the mass and microphone forming a first air pressure chamber with the flexible support for transmittal therethrough of air pressure waves from the resonating mass to the microphone, the microphone arranged to produce an electronic signal when it detects changes in air pressure from the pressure waves traveling through the chamber.

Abstract: An alarm for indicating movement of a golf bag to preclude theft. The inventive device includes an elongated support stanchion positionable within the bag. An alarm assembly is coupled to an upper end of the stanchion and shaped so as to resemble a golf club head. The alarm assembly can be remotely armed and operates to sense movement of the bag to sound an alarm and prevent theft of the bag or clubs contained therein.

Abstract: A shock sensor includes an inductance coil, a magnet, a magnetically soft material, and a support bracket for the magnetically soft material. The inductance coil and the magnet are fixed relative to each other. The magnetically soft material has one side thereof fixed on the support bracket and lies relative to the coil and the magnet so that the magnetically soft material can move up and down as well as leftwardly and rightwardly and inwardly and outwardly when the shock device vibrates and thereby alter a magnetic flux from the magnet to the inductance coil so as to generate signals responsive to the fluctuations of a magnetic flux.

Abstract: The device comprises a flat and elongated condenser with a piezoelectric dielectric material placed between two electrodes. This condenser is fastened to a barrier surface such as the glass pane of a display, a cupboard, or a glass window of a protected space. The condenser is connected with an electrometric amplifier, the signals of which are transmitted to an electronic alarm unit. When the glass pane is subjected to shocks or to mechanical stresses due to an attempted break-in, the condenser will generate electrical signals able to trigger an alarm when they exceed a certain threshold. The condenser and the amplifier may also be adjusted so as to trigger an alarm when the electrical field is modified by the movements of a dielectrical body within the protected region.

Abstract: Dual microphones and a time-of-arrival processing circuit comprise a direction-sensing system which improves the false alarm immunity of an acoustic glass break detector by restricting its coverage to a well-defined zone. By comparing the arrival times of an abrupt sound at two spaced microphones, the processing circuit determines the direction of the sound. If the sound originated in the intended coverage zone, the processing circuit generates a signal which enables the glass break detector; otherwise, the detector is inhibited. When the improved glass break detector is oriented so that potential false alarm sources are outside the coverage zone, false alarm immunity is enhanced.

Abstract: A motion sensor for use with a security system provides an output signal to initiate an alarm whenever a significant level of movement is detected by the motion sensor. A light emitter directs light through an optical path onto a light detector, which generates an electrical output signal in response to the light directed onto it. A resiliently supported mass is coupled to the optical path to modify the optical path in response to motion imposed upon the mass, thereby reducing the transmission of light in the optical path and affecting the electrical signal as the mass moves. The motion sensor of the present invention is responsive to movement in all directions, and, since it is optical in nature, is immune to the presence of magnetic fields.

Abstract: A portable automobile alarm hung over the top of an automobile side window is secured in place by raising the window into its frame. The portion of the unit positioned on the interior side of the glass contains a sensor, a receiver, and associated electronic circuitry. The exterior unit houses an alarm siren. The unit is powered from an internal battery or from a cigarette lighter. The unit may be armed and disarmed by a remote transmitter.

Abstract: An electronic alarm system using graphite sensor will be activated when the sensor is either cut, shorted, or touched. A rapid change of the sensor signal will be detected by a differential section when the sensor is touched, but not a slowly drifting sensor signal when the sensor is not touched. A comparing section takes positive or negative signal to activate the alarm system by sending a signal to a output section.

Abstract: A safety apparatus for a passage controlled by means of a first member and a second member, has a first device for detecting opening of the passage, a second device for detecting fierce knocking on the first and second members and a third device for detecting abnormally high temperature. The first device detects relative movement between the first and second members. The first device has (a) a block being attached to the first member and having a curved surface, (b) a detector having a casing attached to the second member and a pin having a free end so that the pin is in various positions relative to the casing when the free end of the pin is in various positions against the curved surface of the block as the first member is moved relative to the second member and (c) an alarm actuated by means of the detector for warning of the relative movement between the first member and second members.

Abstract: An aftermarket mechanical shock detector for mounting to protected property containing an existing alarm system. The shock detector incorporates a piezoelectric transducer detecting mechanical vibration and generating an electrical vibration signal, and circuitry for comparing the vibration signal to thresholds. The shock detector includes two separately adjustable thresholds. If the vibration signal exceeds either threshold, the shock detector creates an electrical connection between two terminals, thereby triggering a previously-installed alarm circuit to create an alarm.

Abstract: Apparatus and a method for detecting glass breaking from an impact. Low frequencies are detected that are characteristics of the glass flexing from the impact, and high frequencies are detected that are characteristic of a) the sound of the impact and b) the glass breaking. An alarm signal is issued when the low and high frequencies occur in a predetermined sequence, and have appropriate durations, that are characteristic of glass breaking events. More specifically, the alarm signal is issued only when the detected low frequencies last for a minimum duration on a sliding scale related to their magnitude. Weaker signals must last longer.

Abstract: A transducer cable includes an inner conductor, an outer conductor, and dielectric between the inner conductor and the outer conductor. A longitudinal passage and a sense wire loosely disposed therein extend through the dielectric. Movement, (e.g., intruder-caused vibration) of the transducer cable results in movement of the sense wire relative to the outer conductor, causing corresponding changes in characteristic impedance of the sense wire. A carrier signal transmitted down the inner conductor produces an electromagnetic field that couples energy to the sense wire. The change in characteristic impedance causes reflection of some of the coupled energy, which produces a corresponding signal that is sensed by a receiver circuitry. The receiver circuitry produces a signal indicating the occurrence of the intruder-caused vibration.

Abstract: A transducer cable includes an inner conductor, an outer conductor, and dielectric between the inner conductor and the outer conductor. A longitudinal passage and a sense wire loosely disposed therein extend through the dielectric. Movement, (e.g., intruder-caused vibration) of the transducer cable results in movement of the sense wire relative to the outer conductor, causing corresponding changes in characteristic impedance of the sense wire. A carrier signal transmitted down the inner conductor produces an electromagnetic field that couples energy to the sense wire. The change in characteristic impedance causes reflection of some of the coupled energy, which produces a corresponding signal that is sensed by a receiver circuitry. The receiver circuitry produces a signal indicating the occurrence of the intruder caused vibration.

Abstract: In a glass break detector, noise is removed by averaging the signal before it is analyzed for the characteristics that typically accompany glass breaking events. Low frequency signals, associated with glass flexing before it shatters, are isolated from repetitive or symmetrical noise in the same frequency range to increase the signal-to-noise ratio of the detector, improving sensitivity to valid glass breaking events and reducing false alarms.

Abstract: A motion monitor which produces audible sound representative of motions of a subject or object being monitored, including a carrier, an optical fiber carried by the carrier, a laser source for injecting a laser beam in the optical fiber to produce a speckle light pattern at the output of the optical fiber, a photodetector for producing an output signal representative of modal noise developed in the optical fiber due to physical movement of the fiber, an amplifier for amplifying the output of the photodetector, and a loudspeaker which converts the amplified signals to audible sound representative of the modal noise at the fiber output. Optionally, the signals produced by the photodetector are shifted to a higher frequency range, e.g., the 500-700 Hz range, thereby to enable use of conventional inexpensive electronics and efficient loudspeakers.

Abstract: A sensing cable element including a non-uniform cable which is configured so as to substantially vary along its length in its ability to detect mechanical disturbances.

Abstract: A motion detector having a motion sensitive switch, timing circuit, encoder and radio-transmitting circuit in a housing which may be affixed to a remotely-positioned article; and a decoding and receiving circuit housed in a second housing. The radio-receiving circuit receives the encoded transmitted signal and couples it to a decoding circuit; the decoding circuit is connected to a latch circuit which drives an alarm. The sensitivity of the alarm generation circuits are controlled by a timing circuit, and the alarm may be disabled in order to enable the operator to evaluate the nature of the incoming signals.

Abstract: A remotely-monitored stored-audio security system has a local control unit at a monitored premises that communicates with a remotely located central control unit for alerting personnel of an alarm at the premises. Microphones located on the monitored premises receive sounds that are recorded on a recording device in the local control unit. When the alarm occurs the recording device ceases recording, thereby preserving any sounds that occurred prior to and immediately after the activation of the security system. A detector monitors the input to the recording device and detects the occurrence of a discrete sound, i.e., a sound exceeding the level of ambient noise. When the local control unit transmits the alarm indication it also transmits an indication to the central control unit for informing personnel whether any discrete sounds have been recorded.

Abstract: A door locking device has a shaft portion, a non-skid end portion adjustably connected to a lower end of the shaft portion, a door handle engaging bracket affixed to an end of the shaft portion opposite the end portion, and an alarm device mounted to the shaft portion so as to be responsive to shocks affecting the door handle. The alarm device has an audio output. The shaft portion includes an arcuate shape extending outwardly from the bracket, a straight section extending from the arcuate shape, and an angled section extending vertically downwardly from the straight section. The end portion is threadedly received by the angled section. The bracket has a generally U-shaped configuration with a prong formed interior of the U-shaped configuration.

Abstract: A vehicle detector is disclosed wherein either a glass breakage signal or a door opening signal causes an alarm. The glass breakage signal is caused by the detection of high audio frequency simultaneously accompanied by the detection of a positive pressure change. The door opening signal is generated by the detection of a negative pressure change, which is not preceded by a positive pressure change.

Abstract: A high security ultrasonic receiver apparatus including a rigid metal faceplate having an ultrasonic sensor affixed to the rear side thereof and adapted to sense acoustical energy transmitted to the faceplate. The faceplate has no apertures through which acoustical energy is intended to be communicated to the transducer. All acoustical energy is mechanically coupled to the transducer. The plate is further adapted to be affixed to a wall or wall receptacle in a manner similar to that of a standard electrical switchplate or plug socketplate. The transducer and associated electronic components are adapted to be electrically connected to a remote annunciator in a conventional manner.

Abstract: An electronic article surveillance tag which is responsive to forces applied to the tag's housing. The tag has a piezoelectric film which is attached to the tag housing in such a way that forces which are applied to the tag housing are mechanically coupled to the piezoelectric film. The piezoelectric film generates a voltage which is proportional to the forces mechanically coupled thereto. An alarm detecting means compares the voltage generated by the piezoelectric film with a predetermined reference voltage, and initiates an audible alarm when the voltage generated exceeds the predetermined reference voltage.

Abstract: An optical transducer, such as used in an ultrasound system, includes a signal laser which generates an optical signal the frequency of which varies in correspondence with acoustic energy incident on the transducer. An optical cavity in the signal laser is disposed such that incident acoustic energy causes compression and rarefaction of the optical cavity, and this displacement varies optical frequency generated by the laser. A laser pump coupled to the lasing medium is adapted to apply selected levels of excitation energy appropriate to the generation and detection of acoustic pulses. The signal laser alternatively is adapted such that the refractive index of the optical cavity is varied in correspondence with the incident acoustic energy to modulate the optical frequency of the light generated by the signal laser.

Abstract: An improved electronic article security system is employed for detecting the presence of a security tag within a detection zone. The system includes a transmitter for generating electromagnetic energy and, in the disclosed embodiment, a single antenna for emitting electromagnetic energy received from the transmitter to establish an electromagnetic field within the detection zone and for sensing disturbances within the electromagnetic field, including disturbances resulting from a security tag within the detection zone. A receiver is provided for processing signals from the antenna relating to sensed disturbances and for providing output signals. A data processing and control section analyzes the output signals from the receiver and determines whether a sensed disturbance within the electromagnetic field is caused by the presence of a security tag within the detection zone.

Abstract: A glass break simulator responds to a low-frequency sound component of the sound of breaking glass produced by striking the glass. The glass break simulator detects the low-frequency sound component and when an amplitude of the low-frequency sound component exceeds a predetermined threshold value, the simulator generates a high-frequency sound component by converting a digital representation of the high-frequency sound component into sound. The low-frequency sound component and the generated high-frequency sound component are directed at a glass break detector to test it, with the glass break detector responsive to both low and high-frequency sound components.

Abstract: Apparatus utilizing change in pressure condition in an area to be protected to indicate intrusion or change in conditions of the area by using a pressure detection device to detect pressure waves at low and infrasonic frequencies which includes a pressure transducer sensitive to change in pressure to provide an output signal. In some instances an amplifier is provided to amplify the output signal, a signal conditioning circuit is provided to delay a portion of the signal, and a detector device is provided to detect the signal with a comparator provided to compare the signal with the delayed signal and actuate an alarm..Iadd.Additionally, a device producing signals responsive to pressure waves and selected sonic frequencies is taught. If the signals are coincidently received at a coincidence detector, an alarm is activated. Further, the signals can be stretched and/or delayed before receipt at the coincidence detector. .Iaddend.