Technical Description

  1. Basic Concept

    Many high theft expensive electronic goods, like computers, printers, monitors, TV, stereo systems, are seldom moved after they are put in place. The new patented invention, an Anti-theft Cord, prevents theft of electrically powered apparatus by detecting the physical removal of the equipment’s power plug from an electrical power outlet, then setting an alarm state that must be reset for the equipment to operate.

  2. Goal of the Concept

    The goal was to develop a sensor system which would detect the equipment’s power plug as it was being removed from the socket thus setting an alarm. The system would be extremely difficult to defeat during theft, but unnoticed by the owner during normal operation, and very immune to creating false alarms. When manufactured as part of the equipment it would be inexpensive, make the equipment inoperable if in the alarm state, and render the device useless. Two sensors have been developed. A first generation mechanical device offers simplicity of design and versatile applications. The second generation sensor uses optical techniques and has no moving parts, is very robust, and self calibrating to all socket types, but it still uses very few inexpensive parts.

  3. Further Description of Theory

    While many anti-theft devices have been developed these are expensive or difficult to install, very prone to false alarms (e.g. movement sensors), involve restrictive and unsightly mechanical restraints, and in general are relatively easy for even unsophisticated thieves to overcome. The Anti-theft power Cord (ATPC) prevents theft by detecting the physical removal of the equipment’s power plug from an electrical power outlet. When changes are detected within the socket, that no thief can prevent, these changes are communicated from the sensor to a control system by a signal on wires in a power cord. When the power plug is removed the imbedded control system will activate an alarm, typically a sound signal. In addition the alarm system can prevent the equipment from operating until the alarm is deactivated.

    The alarm can be deactivated only by password sent to the controller (either by the equipment or an external remote control) which the owner can use when the apparatus is to be unplugged. Reconnecting the plug will not stop the alarm unless the password is entered. The alarm system will also detect cutting of the electrical cord or attempt to remove the cord from the equipment. The alarm system will not be activated by a power failure to the outlet, or any movement of the apparatus that does not require unplugging the power cord; this prevents the most common false alarm situations. The alarm can be easily applied to all equipment. When integrated into equipment it can use remote control, or built in communications lines, to reduce the system cost.

    In the alarm state will simple programs in the microcontroller prevent the device from operating. This makes stolen equipment unusable, substantially reducing the incentive for theft. Equipment during shipping can be put in this alarm state so that only those with the password can use the device.

    A design compliment is an ATPC special multi-socket power bar or extension cords that can activate an alarm on equipment plugged into it when that extension itself is removed from the wall outlet.

  4. Intellectual Property

    • G. Chapman and M. Zaacks, US. patent issued Nov.21, 2000,
    • Canadian Patent applied for February 2003
    • European patent was issued on May 21, 2003 with UK, France and Germany
    • Japanese patent applied for in August, 2003
    • G. Chapman and M. Zaacks, Singapore patent issued Sept. 30, 2005

  5. Technical Details

    The basic concepts of the anti-theft power cord have been given in the previous section and the original US patent. This section describes recent advances in the power cord project which is the development of an Optical Anti-theft Power Cord. The original project developed a mechanical based sensor fitted in the ground plug of a power cord. This used a spring loaded non-conductive rod connected to a microswitch. When the plug was in a power socket the rod was pushed back and the switch closed. When the plug was being removed the spring would push the rod forward (keeping in contact with the bottom of the socket) and would be activated in when the rod moved far enough (about 3-4 mm depending on the socket). Hence activation occurred while the plug was still within the socket. While this design was very simple and appeared to be quite reliable, it did have several disadvantages:

    1. the use of mechanical parts makes it potentially prone to mechanical failure
    2. mechanical parts are more complex to assemble
    3. a few sockets were found in which the rod needed a position adjustment to get the best on/off state conditions.

    While such adjustments were built in to the design (a simple screw type adjustment) it would require the user to occasionally do that for a few new specific sockets. The plan for a second generation device was to overcome these restrictions, and improve the device.

  6. Second Generation Sensor (Optical Anti-Theft Power Cord)

    The important advantage is the creation of a non-mechanical system with no moving parts that would retain all the advantages of the earlier design. Making an optical sensor within the ground research was started in 2003. To detect removal of a plug with an optical sensor, an InfraRed (IR) reflection sensor set, consisting of an IR LED and a phototransistor, has been mounted within the ground prong of a standard 3-prong plug. When the reflectivity of the socket surface changes as it is moved from the socket, the output level of the phototransistor will vary correspondingly due to the changes in the magnitude of reflected light. Therefore when the plug is removed, we can detect the change in the output of the phototransistor and trigger an alarm. As with the mechanical system by building the optical sensor into the ground prong it retains the important feature that detection occurs while the sensor is still within the socket, making it extremely difficult to bypass or defeat.

    Low cost commercially LED/Phototransistor sensors that fit within the prong were used in this work (price in lots of 1 about $1). Tests were done on over ten socket types (ranging from black, multi-coloured to white) measuring the behavior of the sensor as it was removed from the socket. From this a design and algorithm was developed which will detect the change of the sensor position within a small motion (few mm) for all sockets. Versions with one and two sensors mounted on a small printed circuit board have been created.

  7. Commercial Prototype

    To demonstrate the Optical Anti-Theft Power cord a commercial style prototype has been created. The operating principals are the same as the second generation sensor but with significantly reduced size and enhanced capabilities. As Figure 1 shows, in the commercial prototype the power connection plug end integrated optical sensor and controller were reduced to fit within a standard plug. The optical sensor fits well within ground prong of a standard plug. The sensor and the controller are integrated into a single simple printed circuit board. The controller portion sits on an 11x11 mm section. Figure 2 shows the integrated optical sensor and controller board fits within a standard power plug case. Figure 2 shows the equipment end plug of the Anti-theft power cord. Note the addition of two small connectors at the equipment end plug which communicates through a modified equipment socket to the equipment end master controller. Figure 3 shows the equipment end master controller, built into a box containing an equipment power socket. The equipment power socket is of standard North American size but slightly modified to mate to the Anti-Theft equipment end plug communications lines. The communications lines also power the integrated optical sensor and slave controller enabling the wall end plug sensor system size to be reduced significantly from earlier development prototypes. Note that this design retains the master controller at the equipment end, slave controller at the plug end with communications between them. Hence alarm activation will occur either by removal of the plug or by cutting the cord.

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    Figure 1: Anti-theft plug, showing the integrated sensor and slave controller fit within a standard plug.

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    Figure 2: Anti-theft equipment end plug. Note the addition of the communication connectors.

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    Figure 3: Commercial prototype equipment end socket (bottom) and master controller box.

    The optical system is self calibrating to all types of sockets. When the plug is inserted and activated the sensor does an initial calibration (taking 8 seconds) of the optical parameters for that socket. Note these values will not change significantly while the sensor is within the socket. Alarm conditions are tested 10 times per second. This design is very stable. It is not affected by moving the socket, or pulling on the plug, only by removing it. The worst case socket found allows at most a 4 mm removal before an alarm occurs, far less than the 23 mm length of the ground prong on the plug. Thus alarm activation always occurs before the plug is fully removed from the socket.

    The commercial prototype has added several important advances. In any product using the ATPC, the master controller has been moved to within the power supply for the equipment, resulting in a significant reduction in power cord sensor size and part count. It has also enable a single backup battery to power the system in the event of the alarm state for in excess of 30 hours, or when in standby state during power failures about 60 hours, with more advanced power savings programming this could be significantly extended. The batteries are recharged from the power source and do not need to be replaced. An additional feature is the option to have the alarm state cut power to the equipment so no operation of it is possible.

    Note that this commercial prototype is designed for demonstration purposes and as such is much larger than any system would require. Equipment with the ATPC integrated into the design requires few additional parts as over 90% of the master controllers devices exist already in the majority of electronic control systems. For example the commercial prototype the power source would be unnecessary with the equipment’s power supply. The microcontrollers used are very simple and cheap (less than $0.50 each in small lots). The prototype master controller can easily be replaced by adding programming to an already embedded microcontroller in most equipment.

  8. Conclusions

    The optical sensor has successfully replaced the mechanical sensor first generation version removing all limitations of the mechanical system while retaining all the previous advantages within the patent claims. The commercial prototype has extended this by significantly reducing the plug end integrated sensor/controller size; retaining all the features of the optical sensor and adding additional features to the master controller.

    1. Optical sensor has no moving parts, removing potential failure points.
    2. The optical sensor uses only off the shelf parts and printed circuit board technology reducing production costs.
    3. The optical detector is self calibrating for all socket types removing any need for adjustments.