Abstract: A wire fence alarm system 10 comprises a plurality of zones in which a wire or set of wires is stretched between two anchor posts. A sensing post includes sensors for detecting deflection of one of the wires and a processor for generating alarms responsive to signals from the sensors. One or more of the anchor posts comprise rotating members attached to the wires. Use of the anchor post to climb the fence will result in an imbalance in the forces applied to the rotating members by the wires, thereby initiating an alarm condition.

Abstract: A security system (10), operable to produce an ALARM signal indicative of glass breakage in a region (16) in which a human being (24) may legitimately be present, has a human presence detector (12), a glass breakage detector (14), and an alarm signal activator (30) that includes a one-shot timer (52). A HUMAN PRESENCE DETECT signal (36, 38) output from the human presence detector triggers or retriggers the timer to produce an active output for a predetermined holdoff time interval T.sub.H. The active output causes a gate (58) to prevent a glass breakage alarm or GB DETECT pulse (46) from the glass breakage detector from reaching a control panel (34) and thus from triggering the ALARM signal if the GB DETECT signal occurs within the holdoff time interval after a HUMAN PRESENCE DETECT signal. Another gate (64) prevents a GB DETECT pulse (48) from reaching the control panel if that pulse occurs while the human presence detector is detecting human presence in the region (38).

Abstract: A piezoelectric detecting system for detecting the opening of an enclosure without the need of an external battery or electrical system is disclosed. Several different piezoelectric sensor configurations to effect the detecting system are disclosed.

Abstract: A processor, such as a microprocessor, responds to the detection of an input audio signal generated by glass breakage to cause an alarm to be indicated, such as at a remotely located alarm control panel. The system determines when the input power supply voltage supplied to the system falls below a selected low voltage level. The system is placed in a test mode of operation in response to a uniquely characterized, humanly generated input sound signal and then can be tested by any appropriate humanly generated input sound signal. The system continually monitors ambient background noise and determines when an absence thereof occurs so as to provide an indication of such absence to alert the user to the possibility that the system may have been purposely comprised. The system further uses a number of indicators arranged so that the meanings thereof are different depending on whether the system is in an alarm detection mode of operation or in a test mode of operation.

Abstract: An assembly for protecting a conduit having a core and an axial length, which length is susceptible to being pinched by a structure is disclosed. The conduit includes an insulating coating in surrounding relationship about the core, with the assembly including a semiconductive layer in surrounding relationship about the insulating coating, and a switching layer in surrounding relationship about the semiconductive layer. The semiconductive layer being formed from partially vulcanized ethylene propylene rubber including particles of a conductive element in the form of carbon black, silver, nickel, aluminum or the like. The switching layer is non-conductive in its unstressed state and conductive when pinched such that the switching layer completes a current flow path between the semiconductive layer and either a grounded structure or another conductive layer, which condition may then be detected.

Abstract: A pair of spaced elongate primary security members extend in a first direction, and each has a plurality of longitudinally spaced openings. The ends of a plurality of elongate secondary security members, extending in a second direction which is transverse to the first direction, are located in aligned openings in the primary security members. The ends of the secondary security members are thereby held captive in the primary security members. The secondary security members span a space between the primary security members, and the secondary security members are thus spaced apart from one another. A tertiary security member supports the secondary security members between the primary security members. An electrically operable burglar protection system, having an alarm, is connected to the security members.

Abstract: A sensor has a reduced probability of generating a false alarm in the presence of a strong high frequency acoustic wave, such a false alarm being caused by the saturation of the microphone which is part of a single microphone glass break sensor. The sensor improves an alarm system's immunity to false alarms by using two microphones instead of one, wherein each microphone is used in combination with a filter and a signal processing stage to detect one of the characteristic components of an acoustic wave generated in a glass break event. The microphone used to detect the low frequency component is fitted with an acoustic filter which attenuates the high frequency component of the wave. This reduces the probability of a false alarm by ensuring that the low frequency electrical signals fed to the alarm system's logic and timing circuit are generated by an external event rather than by the microphone itself.

Abstract: A security enclosure comprises a first layer of an insulating material extending over the whole of the area of the enclosure and carrying a linear electrically responsive element on at least one surface. A low tensile strength layer having lower cohesion than adhesion is located between the first layer of insulating material and the electrically responsive element. A second layer of insulating material is adhered to and covers the electrically responsive element. The element is arranged in a configuration on the surface so dividing the surface that attempted penetration of the enclosure changes an electrical characteristic of the element, the change being detectable by an electrical circuit. An attempt to remove the second layer of insulating material to gain access to the element results in breakup of the low tensile strength layer and thus damage to the element and produces a detectable change in an electrical characteristic of the element.

Abstract: There is disclosed a security enclosure including a folded, flexible, electrically insulating sheet extending over the whole of the area of the enclosure and carrying lines of electrically responsive material on each side, the lines defining a conductor extending over both sides of the sheet, electrical connections between lines on one side of the sheet and respective lines on the other side of the sheet being provided by line connections extending through the sheet and at selected edges of the sheet the line connections being spaced inwardly of the edge and separated from the edges by a respective line-carrying portion of sheet. The enclosure includes a circuit for detecting a change in an electrical characteristic of the conductor caused by an attempt to penetrate the sheet.

Abstract: A combined alarm system and window covering assembly includes a top housing, a bottom rail, a covering, a continuous conductive wire which has a first end and a second end and an alarm device. The alarm device has a first input terminal and a second input terminal. The covering is mechanically coupled to the top housing and the bottom rail. The continuous conductive wire extends from the top housing down to the bottom rail and up from the bottom rail to the top housing. The first and second ends of said continuous conductive wire are electrically coupled to the first and second input terminals of the alarm system. The continuous conductive wire is coupled with the bottom rail as a main pull string for raising and lowering the bottom rail and the covering.

Abstract: A security enclosure comprises a flexible sheet of insulating material extending over the whole of the area of the enclosure and carrying lines of electrically-responsive material on each side. The lines on one side of the sheet extend obliquely relative to the lines on the other side of the sheet and are connected thereto at edge portions of the sheet to form a plurality of conductors so dividing the sheet into a number of relatively small areas so that attempted opening of the enclosure changes an electrical characteristic of the conductors. Connectors are provided at an edge portion of the sheet for individually connecting the conductors to a detector for detecting the changes in the electrical characteristic of the lines. The connectors include a switch arrangement which is selectively configured to connect further connectors associated with the detector with selected conductors.

Abstract: A glass break detector for detecting the breaking of a window or the like includes an acoustic transducer having a wide band frequency response, coupled to a dual channel filter and signal processing circuit. A low frequency channel detects an initial positive compression wave caused by the inward flex of the window and a high frequency channel detects the acoustic spectrum which is characteristic of breaking glass. The two channels are combined in a logic circuit that is timed so that the low frequency positive flex is detected initially with the high frequency component following shortly thereafter. If both timing conditions are fulfilled, an alarm is initiated. Additional circuitry is provided to inhibit the alarm if a negative compression wave is initially detected. The detection sequence is initiated by a loud sound characteristic of breaking glass.

Abstract: In a glass smashing alarm system for generating an alarm when a glass smashing sound is detected, the present invention is directed to reduce the possibility of occurrence of an erroneous alarm, and includes a normal alarm mode in which a preliminary alarm is raised for a short time when a glass smashing sound is detected, and a special alarm mode in which a main alarm is raised for a long time when the glass smashing sound is detected, and is constituted in such a manner that mode switching is effected so as to shift the mode to the special alarm mode at the end of the preliminary alarm, and to return it to the normal alarm mode after the passage of a predetermined time if the glass smashing sound is not detected at the end of the main alarm or during the special alarming mode. In another aspect of the invention, generation of an alarm is inhibited if a key unlock switch is turned ON before passage of a predetermined time from detection of the glass smashing sound.

Abstract: A removable safety barrier erectable around the perimeter of a swimming pool or the like including a plurality of upright barrier elements positionable end-to-end around the pool and an alarm arrangement for detecting relative movement between adjacent barrier elements as when a child attempts to enter the pool. Electrical connection between adjacent barrier elements for the alarm is automatically made each time the device is erected around the pool. Improved resistance to tearing, ripping or pulling the restraining mesh from support members is also provided.

Abstract: To monitor for the formation of a crack in a metal wheel such as that of an aircraft tire and wheel assembly the wheel is provided with an optical fiber arranged to extend no-rectilinearly in a position of the wheel surface selected to be preferential for the development of a crack; preferably the preferential region for crack development is the tire bead seat region and the optical fiber is arranged to extend non-rectilinearly around the circumference of the tire bead seat region thereby to lie interposed between the wheel and tire.

Abstract: A fiber optic crack propagation measurement apparatus including an input optical fiber for receiving light energy and an output optical fiber connected to deliver light energy to a detector is disclosed. A plurality of shunt optical fibers are connected in parallel between the input and output optical fibers. The input optical fibers, output optical fibers and shunt optical fibers are secured to a structure in which stresses are expected to cause the advancement of a crack. As the crack grows, individual shunt fibers are broken, reducing the amount of light energy delivered to the detector. Detector signals are generated indicative of the light energy received thereby to report the advancement of the crack. In one embodiment, wavelength division multiplexing techniques are employed so that multiple crack measuring units can be monitored over a single monitoring optical fiber.

Abstract: A glass breakage detector utilizes a single microphone or piezoelectric element as a transducer to detect both the structurally-transmitted vibrations and airborne sounds indicative of breaking glass. The structurally transmitted component and airborne component are combined in accordance with a time-dependent function to provide an indication of breaking glass which has a low false alarm rate.

Abstract: A tamper-proof device for detecting opening and closing events of a secure container is characterized by a fiber optic cable having a first portion connected with a fixed member of the container and a second portion connected with a movable locking member of the container so that the cable is bent or flexed when the container locking member is moved between open and closed positions. Light pulses are transmitted through the cable and variations in the pulses resulting from bending of the cable are detected to indicate opening and closing of the container.

Abstract: An expandable entry detection screen is for use with an electronic alarm system. The expandable entry detection screen includes a first screen frame and a second screen frame for fitting into an opening of a window frame. The second screen frame is adjustably and slidably coupled to the first screen frame. The expandable entry detection screen also includes a first screen mesh and a second screen mesh which are mechanically coupled to the first and second screen frames, respectively. A first portion of a single wire is mechanically coupled to the first and second screen meshes and disposed in the first frame. A second portion of the single wire has slack and is disposed in the second frame. The single wire is electrically coupled to the electronic alarm system. A take-up mechanism takes-up the slack in the second portion of the single wire. The take-up mechanism includes a mounting bolt and nut assembly, a spring and a hook. The mounting bolt and nut assembly is mechanically coupled to the second frame.

Abstract: A sensing element (18) for use in an alarm system for protecting an area enclosed by flexible closure device (10). The element includes a plurality of conductors (16), at least one of which is a decoy conductor intended to prevent circumvention of the alarm system by short-circuiting or the like. The decoy conductor can be a dummy conductor carrying no current, or can be connected into an alarm circuit arranged to sense attempts to connect the decoy conductor to another conductor.

Abstract: An electrical conductor element in the form of a flexible or rigid sheet is provided for detecting attempts to break into a space where valuables or money are being stored, such as a strongroom or the coin container of a slot machine. The base material of the element is in the form of a woven or non-woven material or of plastic sheeting, and the electrical conductor is in the form of wire such as enameled copper wire for electrical connection with an alarm system. The conductor is secured in place by stitching, that is to say the wire is either formed into penetrating stitches by being fed from the needle or shuttle of a sewing machine or it is fed from a stationary part of the sewing machine so as to be fixed in place by stitches or conventional textile yarn or thread. When the conductor is interrupted by drilling, sawing or the like the alarm system is activated.

Abstract: A security screen assembly comprises a screen of mesh material with an optical path formed from at least one optical fiber integrally interwoven with the screen material in a generally serpentine path. A light source or transmitter is coupled to the first end of the optical path while a suitable light detector is coupled to detect light emitted from the second end of the optical path. An interface unit connects the screen to a remote alarm control unit for activating an alarm if the detected light signal falls below a predetermined intensity.

Abstract: A flexible connection is made between the printed conductor array of an automotive windshield or rear window and an electric cable by a braided body formed with a lug at one end for connection to the cable and having, at the opposite end, oppositely bent arms or feet in the form of arms of a T soldered to the conductor array only at the extremity of these feet.

Abstract: Optical fibers are used for monitoring the structural integrity of space based or aircraft structures where prompt notification of damage is required to effect rapid repair and thereby maintain safety and operational reliability. A plurality of optical fibers are disposed in an X-Y relationship, with the fibers optimally placed in a pattern comprised of multiple path reversals which provides extensive area coverage with a minimum of fibers thus defining multiple zones wherein damage within a zone is determined by interruption of the light through the damaged fibers.

Abstract: A fiber optic detection system comprising an array of fiber optic elements is presented. Each fiber optic element is uniquely encoded using a plurality of discrete ferquencies, digital codes or other encoding techniques. When a break occurs in one or more fiber optic elements, the missing light frequencies or digital codes are sensed, thereby indicating the break. Preferably, the fiber optic elements are arranged in a grid pattern so that precise location of the break can be made.

Abstract: The present invention is a kit which contains components for an alarm screen assembly. The kit includes a screen mesh which is formed from a sheet of non-conductive screen material and a conductive wire which is mechanically coupled to the screen mesh. The screen mesh has marginal edge portions. The kit also includes a plurality of framing members and frame member-couplers. Each framing member is adapted to secure one of the marginal edge portions of the screen mesh thereto. The framing member-couplers couple the framing members together to form a frame which is to be mounted on a building enclosing structure. The kit further includes a container which includes a tubular member which has a first open end and a second open end. The tubular member is of a predetermined length and a predetermined diameter. The container also includes a first end cap and a second end cap. The first and second end caps are disposed at the first and second open ends of the tubular member, respectively.

Abstract: An electrically conductive security screen includes an electrical resistance sensor and alarm to detect tampering with the screening material of a window. An elongated path of flexible and electrically conductive coating composition is applied to the screening material in a predetermined and non-overlapping pattern, such that a closed circuit loop is formed when it is attached to the sensor alarm; the coating having an electrical resistance that varies when it is distorted or its path interrupted. The pattern having a marginal section of high electrical resistance and being in series with at least one switch.

Abstract: A security enclosure is formed from layers of flexible material. One layer carries a flexible semiconductive line arranged to extend over the whole area of the enclosure. Any interruption of the line by unauthorized opening of the enclosure changes the resistance of the line and so can be detected by a monitoring circuit. Further, two layers of semiconductive fibers also cover the whole area of the enclosure and are separated by an insulating layer. The length of the fibers is greater than the thickness of the insulating layer so that if the enclosure is pierced fibers from one layer will be forced into contact with fibers from the other layer. This will change the combined resistance of the layers and this can also be detected by a monitoring circuit. The two measures can be used separately.

Abstract: The security window is a laminated pair of polymeric panels having electrically conductive rods sandwiched therebetween. Glass fibers, having electrically conductive coatings, extend from edge to edge of the plastic window panels and are distributed in the rods which substantially cover the entire window area. The index of refraction of the coated glass fibers is as identical as possible to that of the surrounding plastics, making the electrically conductive rods substantially invisible. The conductive rods are connected in series. The resistance characteristics of the circuit are monitored to detect damage to the window.

Abstract: A penetration sensor is disclosed which contains first and second transducers sandwiched around a layer which capacitively isolates the individual transducers. This sensing arrangement allows for the operational state of the sensor to be tested by applying an interrogation signal to each of the transducers.

Abstract: A glass fracture detection system includes a circuit having a sensor for providing an output signal when a glass fracture occurs. The sensor is positioned within a housing so that, when the housing is mounted on the surface of the glass adjacent the frame in which the glass is encased, the sensor is automatically positioned in communication with the glass surface at a specified distance from the frame, which distance is selected so as to reduce damping of the output signal due to the presence of the frame and to reduce signals reflected from the frame to the sensor.

Abstract: A security window is a laminated pair of polymeric window panels having waveguides sandwiched therebetween for transmission of ultrasonic compression waves. The waveguide transmission medium is glass fibers extending from edge to edge of the plastic panels and distributed in plastic strips which cover the entire window area. The index of refraction of the glass fibers is as identical as possible to that of the surrounding plastics, making the waveguides substantially invisible. A transducer initiates an ultrasonic compression wave which travels the length of the waveguide, and is detected by a transducer at the other end of the waveguide. The received signal amplitude diminishes when the waveguide is damaged and such change is used to trigger an external alarm system.

Abstract: A surveillance installation to protect an area of ground. A number of sensing units are spaced around the perimeter of the area to be protected. Each sensing unit comprises a network of strands inconspicuously deployed over a portion of the ground and connected to a magnetically operated switch. When an intruder trips one of the strands, the magnetic switch is operated to signal the presence of an intruder. A central monitoring unit powered by a low voltage D.C. supply connects the various sensing units by means of a two-wire circuit. The central monitoring unit includes signalling devices to indicate the location of the intruder. The system also has the capability of initiating intruder warning devices.

Abstract: The present invention relates to a railing selected among hollow railings, grilles, tubes or the like in which a continuous sensor made of an optical fiber extends, which railing is filled with a suitable filling material, the sensor fiber being connected to outside control and/or alarm units to form a complete circuit. The optical fiber has advantageously a numerical aperture (NA) of 0.08.ltoreq.NA.ltoreq.0.5 preferably the following parameters:Bending loss .alpha.exp(-.beta.r), r-Bending radius .beta..alpha.N.A. (b/a) .gamma. b-cladding radius, a-core radius of the fiber, 0.1.ltoreq..gamma..ltoreq.3.0.The filling material has preferably the form of pellets and is suitably selected among glass, steel, ceramics or sand.The railing preferably comprises a binder selected among soft rubber and plastics, e.g. a polyester. The binder may comprise also a material selected among an irritating material and a dye.The railing may also be a system of railing wherein the sensor extends through all the railings.

Abstract: A security installation for a property includes an imperforate protective barrier, a plurality of spaced posts extending upwardly from the top of the barrier and a plurality of spaced trip wires extending between the posts for detecting the presence of an intruder breaching, or attempting to breach, the barrier. The installation further includes a plurality of spaced posts protruding transversely from the inner side of the barrier, and a plurality of electrical wires extending between the posts. The electrical wires are adapted to impart at least a temporarily incapacitating shock to an intruder.

Abstract: A security installation includes a primary barrier section protruding upwardly from a substrate and extending along the substrate in a first direction, a secondary barrier section protruding from, and extending along, the primary section, with the secondary barrier section being movable with respect to the primary barrier section in a second direction extending transversely to the first direction, and sensing means for sensing movement in the second direction of at least a portion of the secondary barrier section relative to the primary barrier section.

Abstract: A signal is received from a key having predetermined information. A discriminator determines whether the received signal from the receiver represents the predetermined information. An actuator performs a predetermined anti-theft operation in response to output signals from first and second detectors indicating that at least one predetermined one of the covering members is closed and locked. The operation of the actuator is disabled in response to an output signal from the discriminator indicating that the received signal represents the predetermined information. The key includes a magnetic element forming first predetermined information, and light emitting elements for emitting infrared ray carrying second predetermined information. The actuator performs the predetermined anti-theft operation in response to an output signal from a third detector indicating that the key has been removed from a predetermined key hole, in addition to the output signals from the first and second detectors.

Abstract: An apparatus for verifying the integrity of a wall automatically sets off an intervention in the case of an act committed against the wall. A capacitive sensor is formed on the external or internal surface of the wall and consists of a thin planar condenser matching the shape of the wall. An oscillator having variable frequency has its control input connected to a plate of the condenser, the other plate being connected to ground, and a circuit detects the variation of frequency of the output signal of the oscillator resulting from a variation of condenser capacitance.

Abstract: A glazing unit alarm system comprising a glazing unit having at least one glazing panel and provided with spaced apart first and second faces and electric alarm means. The electric alarm means comprises a light transmitting electrically conductive coating on the first face and conducting breakable means on the second face. The alarm means are connected in series with the electrically conductive coating and the conducting means to respond to changes in resistance occasioned by a breakage or an attempted breakage of the glazing unit.

Abstract: An alarm actuating sensor device for use in a picket barrier intrusion detection and location system including a generally t-shaped rocker element for rigid attachment to the upper end of a picket and for disposition within the upper longitudinally extending rail providing support for the picket, an elongated rocker spring pivotally engaged at its mid-point by a pin passed through the end of the picket and including downwardly turned end legs for engaging the lower wall of the rail and for exerting a biasing force on the picket pending to resist downward translation thereof, and a length of dual conductor "tape switch" the longitudinal axis of which extends generally along the longitudinal axis of the rail and passes between the rocker element and the rocker spring, whereby downward forces applied to the picket, or lateral forces tending to bend to the picket, cause the tape switch to be pinched between at least one extremity of the rocker spring and a portion of the rocker element thereby creating an electri

Abstract: Procedure for preparing a laminated plate structure having an optical fiber situated therein, in which the optical fiber is situated between two respective laminating agent layers, in turn situated between two glass plates, the optical fiber extending out from the structure at opposite ends thereof. Grooves are cut out of the laminating agent layers around both opposite ends of the fiber extending out form the structure, with tubes being inserted over these respective opposite ends of the fiber and into the grooves, so that the fibers can move freely within these respective tubes. Then, the tubes and adjoining plates are adhered to one another, with appropriate compression being applied to form the final laminated structure.

Abstract: An integrated smoke and intrusion alarm system is provided for windows, doors or other openings in exterior building walls and includes a solar battery charging device and a magnetic test switch. The integrated alarm system is concealed from view and includes a frame assembly with apertures whereby smoke inside the building is easily detected.

Abstract: A security system comprising a signal-carrying member and a detector for detecting a change in the resistance of the conductive path surrounding a core of the signal-carrying member. The conductive path comprises inner and outer layers of semi-conductive tape separated by an insulating layer but interconnected at one end. The semi-conductive tape of at least the outer layer is made of fibrous material such as carbon-leaded PTFE such that when a sharp object pierces the outer layer and the insulating layer, semi-conductive fibers are dragged from the outer layer into contact with the inner layer and form a conductive bridge between the layers.

Abstract: A rectangular sheet of backing material has a first surface and a second surface and a conductive wire which is mechanically coupled to the first surface of the rectangular sheet of backing material. A work of art includes a decorative frame and a stretcher frame which has a first surface and a second surface and which has a rim disposed on its first surface along its peripheral edge and a painting canvas which has a front side and a back side. The stretcher frame includes a plurality of individual frame members which permit each of four peripheral edges of the front side of the painting canvas to be folded over so that the folded over peripheral edge is adjacent to the back side of the painting canvas. The dimensions of the stretcher frame may be expanded in order to stretch the painting canvas. The stretcher frame and the painting canvas are mounted on the decorative frame. A plurality of staples secure the conductive wire to the painting canvas, the stretcher frame and the decorative frame.

Abstract: A security awning window is presented with increased safety factors which grant protection against both adverse weather conditions and unauthorized entry. Alarm struts span the window which, if deflected act as a switch for an audible alarm and also engage the panels to provide increased burglar or adverse weather protection.

Abstract: An intrusion alarm system, for an enclosed space responsive to frequencies in the one to two Hertz range for detecting opening of doors or windows; and responsive to frequencies in the three to four Khz range for detecting breaking glass. A detected frequency in the one to two Hertz range increases the sensitivity required for detecting breaking glass.

Abstract: The present invention relates to a wallpaper which comprises an optical fibre which together with an outside control and/or alarm unit forms a closed optical circuit. The wallpaper is a sheet made from a suitable material, e.g. paper, plastic material and textile fabrics. This material may have the adhesive layer on itself. Alternatively, the adhesive is applied before lamination. The invention relates also to a process for the manufacture of the wallpaper.

Abstract: The present invention is a roll-up alarm screen assembly for use in a frame. The frame has a first magnet disposed in its bottom portion and a second magnet disposed in its top portion. The roll-up alarm screen assembly includes an alarm screen and a roll-up mechanism which rolls the alarm screen up and down. The alarm screen includes a screen mesh and a conductive wire which is mechanically coupled to the screen mesh. The roll-up alarm screen assembly also includes a first magnetic coupler and a second magnetic coupler. The first magnetic coupler electrically couples severed ends of conductive wire when the first magnetic coupler is disposed adjacent to the first magnet. The second magnetic coupler electrically couples severed ends of conductive wire when the second magnetic coupler is mechanically coupled to the roll-up mechanism and is positioned so that the second magnetic coupler is disposed adjacent to the second magnet in order to detect any movement of either the roll-up mechanism or the screen mesh.

Abstract: A monitor system for sensing the failure of a rupture disc and activating an alarm in response to such a failure. The system also senses potential failure of a rupture disc. The system includes a failsafe signal carrying loop which is broken when the rupture disc fails, thereby interrupting the signal. The system also includes a signal sensor which recognizes a signal interruption or substantial modification in the signal and initiates and cooperates with an alarm device to provide notice to an operator or a safety device that the rupture disc has failed.

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.