US3721972A - Ultrasonic burglar alarm system - Google Patents

Abstract

An ultrasonic burglar alarm system employing one or more transmitters on the exterior of the protected enclosure, and one receiver in the interior of the enclosure. An ultrasonic sound transmission path can exist, but normally it is not completed because of the intervening walls and closed doors and windows of the enclosure. Upon opening of any door or window, or any breaching of the walls, the sound transmission path is completed from exterior to interior, the received sound is detected, and an alarm is given. A supervisory circuit employing exterior receivers is also used, so that if an attempt is made to muffle any exterior transmitter or impair any exterior receiver, an alarm is given.

Description

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Hermans 51March 20, 1973 1 ULTRASONIC BURGLAR ALARM 3,s 9,924 3 1971 Dralce etali duo/258 B x SYSTEM Primary Examiner David L. Trafton [76] Inventor: Albert L. Her-mans, c/o Seabord Atmmey HamS Zimmerman Electric, 225 5'Bancroft Ave., San Leandro, Calif. 94577 [57] ABSTRACT [22] Flled: 1972 a An ultrasonic burglaralarm system employing one or [2]] Appl. No.: 228,138 more transmitters on the exterior of the protected enclosure, and one receiver in the interior of the enclo- [52] U S C] 340/276 340/258 B 3 6 sure. An ultrasonic sound transmission path can exist,

1 I 0 y a 340 275 but normally it is not completed because of the inter- 5 H Int Cl Gosh vening walls and closed doors and windows of the enclosure p p g of y door or window or y Field of 258 258 26X breaching'FftheTvalls, the sound transmission path is 340/276' 275 9 completed from exterior to interior, the received sound is detected, and an alarm is given. A superviso- References C'ted ry circuit employing exterior receivers is also used, so

UNITED STATES PATENTS that if an attempt is made to muffle any exterior transmitter or impair any exterior receiver, an alarm lS 2,071,933 2/1937 Miessner ..340/26I given.

3,061,829 10/l962 Roberts ....340/258,R 3,491,332 1/1970 Lomas et a1 .;.....3 40/258B X 10 Claims, 3 Drawing Figures I I2; :7 I

Q SgIB W RECEIVER DETECTOR BANDPASS 6 gRELAY j RECEIVERS 4 AMPLIFIER DEMODULATOR AMPLIFIER I C'RCUIT L AUTOMATIC I 9 SENSITIVITY CONTROL ii r A amaze -AM2::-F.-ER

A RECEIVERS ULTRASONIC POWER MODULATOR J ULTRASONIC TRANSMITTERS H AMPLIFIER OSCILLATOR OSCILLATOR To ALL ELECTRONIC CIRCUITS AC; REGULATED v POWER STAND BY ULTRASONIC BURGLAR ALARM SYSTEM BACKGROUND OF THE INVENTION Many intrusion detection systems have been employed in the past to combat burglary and theft. These systems can be categorized as either space detection systems or perimeter protection devices. The space detection systems operating on the microwave or ultrasonic standing wave principle, have serious disadvantages due to their sensitivity not only to air turbulence causedby heating and air conditioning, but also to ambient sound and vibration. Their most serious drawback is that they permit no human activity inside the protected area. The perimeter protection systems, using door and window switches and conductive tape on glass surfaces can be defeated easily by experienced burglars by tampering with the switches, or avoiding the detectors altogether, i.e., by cutting through a wall.

It is therefore an object of this invention to provide ,an intrusion and burglar alarm system which permits authorized human activity inside the protected enclosure. It is also an object of this invention to provide a burglar alarm system which cannot be circumvented or defeated. It is another object of this invention to provide a burglar alarm system which can'be used in a variety of installations to protect may different kinds of enclosures.

SUMMARY or THE INVENTIO The present invention employs one or more ultrasonic transmitters located on the exterior of the protected enclosure. The transmitters emit modulated ultrasonic sound towardthe enclosure. The enclosure lated sound from the transmitters. The output of the monitoring receivers is checked by a supervisory circuit, which will actuate the alarm if any monitoring receiver is not receiving sound from its associated transmitter. Thus any attempt to defeat the system by muffling the transmitter or impairing the monitoring receiver will cause an alarml Located in the interior of the enclosure is one or more receivers tuned to receive the ultrasonic sound from the transmitters. The sound transmission path must pass through the walls or openings (windows, doors, etc.) of the enclosure. Normally, however, the doors and windows will be closed, and the walls are im- The system is powered by a regulated power supply 1 and a constantly chargedstandby battery 2, which provide power to all electronic circuits. The ultrasonic oscillator 3 generates an ultrasonic signal of a predetermined frequency, on the order of 20,000 Hz, which is fed to the modulator-oscillator 4. The modulator-oscillator 4 modulates the ultrasonic signal from the oscillator 3 with a lower frequency signal, typically 250 Hz. The modulated signal is amplified by the power amplifier 5, and is then conducted to theultrasonic transmitters 6, and thealarm logic circuit 18. Each of theultrasonic transmitters 6 is located exteriorly of the protected enclosure, where it emits the modulated ultrasonic tone toward the interior of the protected enclosure. 7

Located inside the enclosure arereceivers 8 separated from thetransmitters 6 by the wall of theenclosure 9, in which there is acloseable opening 10 such as a door or window. Thereceivers 8 convert all received sound into an electrical signal. Each of thereceivers 8 feeds the signal through a variable resistor l l and amanual switch 12. The resistor 11 controls the sensitivity of eachindividual receiver 8, and theswitch 12 allows the occupant of the enclosure to turn on or off individual receivers. The signal then goes to thereceiver amplifier 13, where it is amplified, and thence to the detector-demodulator 14. There the predetermined frequency of the oscillator 3 is detected, if it is present. That detected signal is also demodulated, producing a signal of the frequency of themodulatoroscillator 4. A portion of the DC. voltage level from the detector-demodulator 14 is sampled by theautomatic sensitivity control 15, which uses that voltage level to control the gain of thereceiver amplifier 13, assuring the constant sensitivity of the system.

The demodulated signal from the detector-demodulator -14 passes through thebandpass amplifier 16, where any extraneous signals are removed, and then to thevariable resistor 17. Thisresistor 17 is a threshold detector which is adjusted to remove any leakage signals that might penetrate the perimeter of theenclosure 9. The adjusted signal then goes to thealarm logic circuit 18 which, when it senses the presence of the demo du latedssignal' indicating the enclosure has been pervious to the sound. If a burglar should attempt to THE DRAWINGS FIG. 1 is a block diagram of the circuitry of the present invention.

FIG. 2 is a representation of a typical mounting of the transmitter and receivers of one embodiment of the invention.

FIG. 3 shows another method of mounting the transmitter in another embodiment of the invention.

is given. Also located exteriorly of theenclosure 9 aremonitor receivers 29 which continually receive the sound emitted by thetransmitters 6. This received sound is converted to an electrical signal by thereceivers 29, and that signal is amplified by themonitor amplifier 30. The amplified signal is detected by thedetector 31, and the resulting DC. voltage is amplified by theamplifier 32. It is then fed to thealarm logic circuit 18. If av would-be burglar attempts to muffle any of thetransmitters 6 or impair any of thereceivers 29, the received signal would be reduced, resulting in a reduced D.C. voltage level going to thealarm logic circuit 18 from theamplifier 32. Thealarm logic circuit 18 senses the 3 reduced voltage, and actuates therelay 19, giving the alarm. i lt should be noted that in a typical installation of the instant invention, everyexterior wall 9 of the protected enclosure would have at least one of thetransmitters 6 mounted exteriorly. Associated with eachtransmitter 6 and installed nearby would be one of themonitor receivers 29. Inside the protected enclosure, each room capable of being entered from the outside would have installed therein at least one of theinterior receivers 8.

It should also be noted thatthetransmitter 6 and themonitor receiver 29 are each mounted inside identical metal boxes. Thus a would-be burglar would have difficulty discerning which unit could be tampered with. Also, each metal box can have a micro-switch tamper sensor mounted just under the cover of'the box, so that any attempt to open either box would result in an alarm being given. FIG. 2 shows a typical mounting of the active elements of the present invention in a home installation. Thetransmitter 6 and themonitor receiver 29 are mounted under theeaves 40 of ahome 41. Thereceiver 8 is mounted on the ceiling of protectedhome 42, and the electronics of the burglar alarm system is mounted in thebox 43. Thetransmitter 4,receiver 29 andreceiver 8 are all connected to thecentral alarm system 43 by amulticonductor cable 44. Of course, if an attempt is made to cut thecable 44, the monitor signal from thereceiver 29 to thealarm logic circuit 18 in thebox 43 would be interrupted and the alarm would be sounded. There may be otheractive elements 6, 29

and 8 connected to thecentral alarm system 43, to protect other'walls and openings of the home.

The embodiment of the present invention shown in FIG. 3 requires only onetransmitter 6 and onemonitor receiver 29. The single transmitter is sufficiently powerful that, mounted atop thebuilding 45, it emits buildings. Considering the reduced number of active elements required, this type of installation would be very economical.

lclaim: I

l A burglar alarm system'for warning of intrusion into a protected enclosure comprising;

ultrasonic transmitter means, located exteriorly of said protected enclosure, to emit an ultrasonic signal ofpredetermined frequency; 7 interior receiver means, located inside said protected enclosure to receive said ultrasonic signal through any opening in said enclosure;

detector means connected to said interior receiver means to detect reception of said ultrasonic signal by said interior receiver means, and to emit an alarm actuating signal if said ultrasonic signal is detected;

alarm means connected to said detector means to sound an alarm upon reception of said alarm actuating signal from said detector means.

2. A burglar alarm system according to claim 1 wherein said ultrasonic transmitter means includes modulating means to modulate the output of said ultrasonic transmitter with a second predetermined demodulated tone of said predetermined frequency is detected.

3. A burglar alarm system according to claim 1 wherein said ultrasonic transmitter means comprises a single ultrasonic transmitter.

4. A burglar alarm system according to claim 1 wherein said protected enclosure comprises a human dwelling place, said ultrasonic transmitter means comprises a plurality of ultrasonic transmitters, each placed exteriorly of every exterior wall surface capable of being breached, and said interior receiver means comprises a plurality of interior receivers, one receiver placed in each room of said dwelling place capable of being entered from the outside.

5. A burglar alarm system according toclaim 4, wherein one or more of said interior receivers includes switching means to selectively switch off and on said receivers.

6. A burglar alarm system according to claim 3' wherein said protected enclosure comprises a human dwelling place, and said interior receiver means comprises a plurality of interior receivers, one receiver placed in each room of said swelling place capable of being entered from the outside.

7. A burglar alarm system according toclaim 6, wherein one or more of said interior receivers includes switching means to selectively switch off and on said receivers.

8. A burglar alarm system according to claim 3 wherein said protected enclosure .comprises a plurality of jewelry cases in a jewelry-store, and said interior .rec'eiver means comprises a plurality of interior receivers, one placed in each of said jewelry cases.

9. A burglar alarm system according toclaim 8, wherein said interior receivers include switching means to individually switch off and on said receivers.

10. A burglar alarm system for warning of intrusion into a protected enclosure comprising;

ultrasonic transmitter means located exteriorly of said protected enclosure, to emit an ultrasonic signal of predetermined frequency;

monitor receiver means, located exteriorly of said protected enclosure to receive said ultrasonic signal whenever said transmitter is operating;

interior receiver means, located inside said protected enclosure, to receive said ultrasonic signal through any opening in said enclosure;

detector means connected to said interior receiver means to detect reception of said ultrasonic signal by said interior receiver means, and to emit an alarm actuating signal if said ultrasonic signal is detected; 7

supervisory circuit means connected to said monitor receiver means to detect continuous reception of said ultrasonic signal by said monitor receiver means, and to emit an alarm actuating signal if said continuous reception is interrupted for more than a predetermined period;

alarm means connected to said detector means and to said supervisory circuit means to sound an alarm upon reception of said alarm actuating sigrial from said detector means or said supervisory circuit means.

Claims (10)

1. A burglar alarm system for warning of intrusion into a protected enclosure comprising; ultrasonic transmitter means, located exteriorly of said protected enclosure, to emit an ultrasonic signal of predetermined frequency; interior receiver means, located inside said protected enclosure to receive said ultrasonic signal through any opening in said enclosure; detector means connected to said interior receiver means to detect reception of said ultrasonic signal by said interior receiver means, and to emit an alarm actuating signal if said ultrasonic signal is detected; alarm means connected to said detector means to sound an alarm upon reception of said alarm actuating signal from said detector means.

2. A burglar alarm system according to claim 1 wherein said ultrasonic transmitter means includes modulating means to modulate the output of said ultrasonic transmitter with a second predetermined frequency, and wherein said detector means includes demodulator means to demodulate said received signal, and to emit an alarm actuating signal only if said demodulated tone of said predetermined frequency is detected.

3. A burglar alarm system according to claim 1 wherein said ultrasonic transmitter means comprises a single ultrasonic transmitter.

4. A burglar alarm system according to claim 1 wherein said protected enclosure comprises a human dwelling place, said ultrasonic transmitter means comprises a plurality of ultrasonic transmitters, each placed exteriorly of every exterior wall surface capable of being breached, and said interior receiver means comprises a plurality of interior receivers, one receiver placed in each room of said dwelling place capable of being entered from the outside.

5. A burglar alarm system according to claim 4, wherein one or more of said interior receivers includes switching means to selectively switch off and on said receivers.

6. A burglar alarm system according to claim 3 wherein said protected enclosure comprises a human dwelling place, and said interior receiver means comprises a plurality of interior receivers, one receiver placed in Each room of said swelling place capable of being entered from the outside.

7. A burglar alarm system according to claim 6, wherein one or more of said interior receivers includes switching means to selectively switch off and on said receivers.

8. A burglar alarm system according to claim 3 wherein said protected enclosure comprises a plurality of jewelry cases in a jewelry store, and said interior receiver means comprises a plurality of interior receivers, one placed in each of said jewelry cases.

9. A burglar alarm system according to claim 8, wherein said interior receivers include switching means to individually switch off and on said receivers.

10. A burglar alarm system for warning of intrusion into a protected enclosure comprising; ultrasonic transmitter means located exteriorly of said protected enclosure, to emit an ultrasonic signal of predetermined frequency; monitor receiver means, located exteriorly of said protected enclosure to receive said ultrasonic signal whenever said transmitter is operating; interior receiver means, located inside said protected enclosure, to receive said ultrasonic signal through any opening in said enclosure; detector means connected to said interior receiver means to detect reception of said ultrasonic signal by said interior receiver means, and to emit an alarm actuating signal if said ultrasonic signal is detected; supervisory circuit means connected to said monitor receiver means to detect continuous reception of said ultrasonic signal by said monitor receiver means, and to emit an alarm actuating signal if said continuous reception is interrupted for more than a predetermined period; alarm means connected to said detector means and to said supervisory circuit means to sound an alarm upon reception of said alarm actuating signal from said detector means or said supervisory circuit means.

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