Abstract: A self-regulating heater including a semiconductor for converting electrical energy to heat. A temperature sensitive element is used to bias the semiconductor as a function of temperature. The heating element has an advantage that its maximum temperature is limited by the biasing network, yet full power is available just below the limit.

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: An intrusion detector is provided having transmission and receiving cables wherein the cables are leaky from an RF standpoint so that a portion of the RF energy from the transmission cable escapes and is picked up on the receiving cable. Both sine and cosine signals are detected. The cables can be buried.

Abstract: An intrusion warning system for protecting a wall or fence, in particular a chain-link fence, against intrusion by cutting through and/or climbing over same. A small-diameter shielded electrical cable, e.g. a coaxial cable or a shielded twisted pair is mounted on the fence and the vibrations of the fence detected by sensing the small electrical field generated when the dielectric material between the conductors of the cable is stressed by the minute flexing of the cable caused by such vibrations. The sensed electric field signal is AM detected, shaped and then processed as to duration and persistence. An alarm indicating an attempted cut-through type of intrusion is activated if a preselected number of signals of very short duration, indicating abrupt disturbances of the fence, are detected.

Abstract: A detector and indicator for burglar alarms is provided wherein passive resonators, each tuned to a different frequency, are employed across each of the normally closed series switches of the burglar alarm. An alternating current generator is connected to the series line and tuned progressively to the frequency of each of the passive resonators. If an open circuit occurs across any of the resonators, a detector circuit detects the high impedance which results and actuates an indicator circuit wherein the indicator is selected for the frequency of the resonator of a particular location. Even if a plurality of switches are open, the selection circuit will be activated for the particular locations of the open switches.

Abstract: A quasi-stationary electric field is produced by means of an oscillator which produces an output frequency in the range of from 1-40 KHz and whose output is connected via a field voltage amplifier to a field wire which is mounted on and suspended between a plurality of fence posts by means of insulators and extends along at least a portion of the perimeter of an area to be protected. The electric field is detected by an antenna or wire whose output is connected to an AM detector via an amplifier. The output of the AM detector is connected to a high gain voltage amplifying and filtering arrangement so that at the output of this high gain amplifier only signals within the relatively low frequency range of from 0.2 to 2HZ associated with movement of an intruder are present.

Abstract: A quasi-stationary electric field is produced by means of an oscillator whose output is connected to a field wire which is positioned within the area to be protected and the electric field is detected by an antenna whose output is connected to an amplifier. An AM detector is connected to the output of the amplifier and the output of the AM detector is connected via a lowpass filter to a high gain amplifying means including a bandpass filter arrangement so that at the output of this high gain amplifier only signals within the relatively low frequency range associated with movement of an intruder are present. The output signal from the high gain amplifier is fed to a threshold circuit which produces an output signal whenever the input signal thereto exceeds a predetermined threshold value, and this output signal is fed to an alarm producing circuit. The frequency of the electric field is in the range from about 1 to 40KHz and is approximately midway between two successive harmonics of the frequency of the a.c.