US3484775A - Theft prevention system - Google Patents

Description

Dec. 16, 1969 w. D.' CLINE l 3,484,775

' THEFT PREVENTION SYSTEM Filed oct. 20, 1965 2 Sheets-Sheet l Dec. 16, 1969 w. D. CLINE 3,484,775

THEFT PREVENTION SYSTEM Filed Oct. 20, 1965 2 Sheets-Sheet 2 I 54T I I 7a Pad/er I United States Patent O 3,484,775 THEFT PREVENTION SYSTEM Wallace Dean Cline, P.O. Box A-6829, Represa, Calif. 95671 Filed Oct. 20, 1965, Ser. No. 498,457 Int. Cl. G08b 21/00, 17/06, 25/00 U.S. Cl. 340-280 3 Claims ABSTRACT F THE DISCLOSURE A theft prevention alarm circuit for appliances is located in a boxwhich is plugged into a standard wall socket, and a standard appliance plug is plugged into the box. Provision is made so that the alarm box s not easily unplugged, and when the appliance plug is removed from the box an alarm is given.

sets in hotel and motel rooms. A recent survey revealed that motels throughout the United States were losing an average of eight percent (8%) of their television installations each year. To avoid this problem, some motel owners have rigidly secured their television sets into heavy pieces of furniture. These arrangements are expensive and frequently impair ilexibility in viewing the television set from the desired location. In other cases, permanent wiring installations have been effected at substantial cost.

The principal object of the present invention is to prevent the theft of television sets or other appliances by the use of an inexpensive warning apparatus which does not require professional installation.

In accordance with an illustrative embodiment of the invention, a small box may be plugged into an ordinary electrical outlet, and the television Set may be plugged in to the box. Suitable arrangements are provided for preventing removal of the box from the wall socket, at least while the television set is plugged in. The television plug, however, may be removed from the box, energizing an alarm circuit by a switching mechanism within the box.

In a preferred embodiment of the invention, the box may contain an oscillator which is normally de-energized, and which is turned on by unplugging of the appliance. The oscillator energizes a remote alarm circuit, suitably located in the managers ofce, and suitable steps may be taken to bar theft of the television set or other appiiance.

The signals from the warning box may be transmitted through the power wiring for the motel, or may b radiated through the air. I

An important advantage of the proposed system is the low installation cost. The warning boxes or units may be plugged directly into the wall outlets, so that expensive custom electrical or custom cabinet installations are avoided. p

Other objects, features and advantages of the invention will become apparent from a consideration of the following detailed description and from the drawings in which:

FIG. l is a diagrammatic view of motel indicating the use of the theft prevention system of the invention;

FIGS. 2, 2a and 2b show the mechanical arrangement of a theft prevention signal generator unit or box;

FIG. 3 is a typical circuit which may be employed ICC to produce a warning signal when the present warning system is energized;

FIG. 4 shows a typical receiver for responding to signals from the theft indication signals; and

FIG. 5 indicates an alternative arrangement for preventing removal of the alarm signal generator unit from a wall socket while the appliances are plugged into the unit.

Referring more particularly to the drawings, three rooms 12, 14, 16 of the motel 18 are shown, in addition to the oice 20. In the motel rooms 12, 14, 16, television sets 22, 24, 26 are located, and they are normally plugged in to respective alarm signal generator boxes 28, 30, and 32. These warning boxes or units are plugged into conventional wall outlet boxes which are in turn connected to the power lines 34.

In the ollice 26, a radio receiver 36 is provided with alarm lights which are selectively responsive to signals from the particular alarm signal generator boxes 28, 30 and 32, as discussed below. Signals from boxes 28, 30 and 32 are either radiated through space to be picked up by antenna 38, or are transmitted. over power lines 34 and the input power lines which are capacitively coupled to the input stages of radio 36.

As indicated in FIG. 1, the plug from television set 22 has been removed from box 28. Upon removal of the plug, the alarm circuitry in box 28 is energized, and the signal is picked up by receiver 36. An audio tone may then be heard at the output of .receiver 36 and a light 42 is illuminated. Suitable arrangements such as afset of tuned circuits matched with the warning signal transmitters in boxes 28, 3) and 32 are employed to selectively energize the lights in the receiver 36.

FIG. 2, together with details 2a and 2b show an illustrative implementation of the boxes 28, 30 and 32 of FIG. l. In FIG. 2, the alarm transmission box 28 is provided with two plug prongs 52 for insertion into a standard wall socket 54. As indicated in the detailed view of FIG. 2b, the prongs 52 are provided with points 56 which prevent easy removal of the unit 28. Removal of the plug-in unit 28 may also be prevented by the alternative shown in FIG. 5 of the drawings.

In the illustrative embodiment of FIG. 2, the alarm circuitry is mounted on the insulating printed circuit board 58. Electrical Contact to the board 58 is made at terminals 6l) and 62 which match spring contacts 64 and 66 in unit 28. When television plug 70 is plugged all the way in, its two prongs 72 and 74 engage the contacts 76 and 78, respectively. Spring contact 76 is flexible, and is biased to engage the contact 80 as best shown in FIG. 2a, when contact 76 is not depressed by prong 72 of the television plug 7l);

Contact arm 80 is connected to spring contact 66 by lead S2; accordingly, when plug 70 is removed, current is applied, over one prong 56, lead 841, contacts 76 and 80, lead 32 through contacts 66 and 62, to the circuit board 58. This completes the circuit to the alarm circuit, as the'other Contact 60 is connected to the other side of the alternating current through contact 64 and the other prong S2 of the unit 28.

The operation of the warning circuitry, once it is energized, will now be considered in connection with FIGS. 3 and 4 of the drawings.

The circuit of FIG. 3 is made up of three principal parts, the power supply 92, the audio oscillator 94 and the radio frequency oscillator 96. These circuits are mounted on the board 58 of FIG. 2, and are energized when power is supplied to terminals 60 and 62.

The circuits of FIG. 3 may be of any suitable form, and may `be of known configuration. As implemented in the present instance, however, the power supply 92 includes a fuse 9S, a filament transformer 100, a full wave rectifier bridge 102, and a filter circuit having capacitor 104, resistor 106 and Zener diode 108 as component parts.

The audio oscillator circuit 94 includes the PNP transistor 110, a suitable 40-300 microhenry oscillator coil 112, resistor 114 and potentiometer 116. With power supply and feedback circuits as shown in FIG. 3, audio frequencies of a few hundred to a few thousand cycles per second may be obtained.

The RF oscillator employs a PNP transistor 118 and has stabilized voltage from the Zener diode 108 applied to the transistor collector. The frequency of the RF oscillator is determined by coil 120 and capacitors 122 and 124. Resistor 126 is in the emitter circuit and is connected to the junction between capacitors 122 and 124 to provide suitable feedback and emitter bias conditions. Base-to-emitter forward biasing current is provided through resistor 128. Audio modulation of the RF oscillator is accomplished by the application of signals from audio oscillator 94 by the network including coupling capacitor 128, resistor 130 and capacitor 132. Modulated RF signals are applied to the power lines or to an antenna of loop type, for example, by capacitor 134.

In the circuit of FIG. 4, the diode 140 represents the detector of 4a radio receiver. The radio receiver is tuned to the RF frequency of the units 28, 30, and 32, which are all tuned to the same RF frequency, but to different audio frequencies. It is, of course, also possible to tune the RF frequency oscillator in each of the units to the intermediate frequency of the radio receiver and to couple from the power lines or antenna directly to the first LF. stage of the receiver.

Detected signals are coupled through transformer 142 t tuned circuits 144, 146, 148, 150 and so forth. These tuned circuits .are connected in parallel, and they are, in turn, connected in series with the speaker 152. When one of the units, such as unit 28 is energized by the removal of a plug, the corresponding tuned circuit 144 is energized, and light 42 in tuned circuit 144 is energized. In addition, a warning audio signal of the frequency of the tuned circuit may be heard from loudspeaker 152.

FIG. shows an alternate arrangement for securing the warning units in position which provides greater flexibility than the use of detents 56 on the prongs of the warning units as shown in FIG. 2. In the units of FIG. 5, the electronics of the warning unit 162 is not shown. For installation, the screw or bolt 164 is removed from the center of a conventional receptacle cover plate 166, the prongs 168 and 170 of the unit 162 are plugged in through the cover plate 166. The unit 162 is then secured in place by inserting the screw 164 into a recess 172 in the unit 162 through a small opening through the rear wall of the unit 162, and into its original threads behind the cover plate 166.

Following securing of the unit 162 in place, the recess 172 is closed by a cover plate 174 which contains openings to receiver appliance plugs 70 and 701 which may be arranged to energize the warning circuitry in much the same manner as described above in connection with FIG. 2 of the drawings. Obvious minor modifications would of course be necessary to adapt the physical and electrical arrangements of FIGS. 1 through 4 to the modified physical structure shown in FIG. 5. Thus, the electrical circuitry could be divided into portions above and below the recess 172, and either one or both of the plugs 70 and 701 could be arranged to energize the Warning circuitry when removed. The advantage of the style of FIG. 5 is that it can be more readily removed and used in a different wall socket when such a change appears to be necessary or desirable.

In closing, it is again noted that an important advantage of the present invention resides in the ease of installation. Because of the unitized construction, no electricians or carpenters are required for special wiring or installation.

It 1s to be understood that the above-described arrangements are illustrative of the principle@ Qf the invention. Numerous other arrangements may be devised by those skilled in the art. Thus by way of example and not of limitation, a simple but very noisy buzzer may be installed in the alarm units. When the appliance plug is pulled out, the unit will set up such a racket that the would-be thief will probably plug the appliance back in. Otherwise, the manager or one of the motel employees will soon hear the audio alarm signal.

What is claimed is:

1. In combination:

an alarm circuit;

a power receptacle including a switch 'which is changed in its state by the prongs of a plug as they are inserted into and removed from the receptacle;

means connected to said switch for energizing said alarm circuit as the plug is removed from said receptacle; and

a small box assembly having electric plug prongs extending directly from its side to plug into a standard .wall socket, containing said alarm circuit, said power receptacle and switch, said box assembly further including means for preventing removal of said box assembly from said standard wall socket following mounting the box assembly into the wall socket and plugging an appliance into the power receptacle on the box.

2. A unitized alarm system for preventing the theft of appliances from motel rooms or the like comprising:

a plurality of box like alarm units each having protruding prongs for directly plugging into standard service outlets in respectively different rooms, each of said units having at least one socket for receiving an appliance plug, electronic circuit means within each unit for giving a unique alarm signal when an appliance plug is removed from a unit, and means for preventing removal of the units from the service outlet following plugging of the units into the outlet and the appliances into the units; and

receiver means responsive to the alarm signal to provide a unique warning signal, corresponding to the unique alarm signal.

3. A plug-in alarm apparatus comprising:

an alarm box;

a pair of prongs extending directly from said box for engagement with a power line receptacle;

an alarm circuit in the box;

a receptacle on the alarm box for receiving an appliance plug;

means for preventing removal of the alarm box from the power line receptacle; and

switch means for energizing the alarm circuit when the appliance plug is removed from the receptacle on the alarm box regardless of the state of energization of the appliance.

References Cited UNITED STATES PATENTS 3,229,300 l/l966 Thompson et al. 340`3l0 X 3,411,150 11/1968 Shulein 340-216 2,562,069 7/ 1951 Stein et al.

2,681,443 6/1954 Caulk.

2,979,706 4/1961i Simon et al 340-224 3,045,226 7/ 1962 Trayner 340-280 3,127,597 3/1964 Lewin et al. 340-280 3,247,502 4/ 1966 Eberts 340-224 X 3,274,578 9/1966 Block et al. 340-310 X 3,289,194 11/1966 King 340-280 JOHN W. CALDWELL, Primary Examiner D. L. TRAFTON, Assistant Examiner US. Cl. XR. 340-224, 216

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