Patent Publication Number: US-6989747-B2

Title: Arrangement and method for detecting unauthorized removal of electronic equipment

Description:
PRIOR APPLICATIONS 
   This is a US patent application that claims priority from Swedish Patent Application No. 0203884-2, filed 23 Dec. 2002. 
   TECHNICAL FIELD 
   The present invention relates to an arrangement and a method for detecting unauthorized removal of electronic equipment that is connected to a power source. The arrangement is arranged between the power source and the electronic equipment and includes a first current recognizing element. The detection of the unauthorized removal is obtained by sensing the level of current that flows to the electronic equipment. 
   FIELD OF THE INVENTION 
   Today&#39;s stores and public premises use more and more audio-visual means for conveying their messages. The audio-visual means may for example be plasma screens and large picture projectors. A problem is that this type of products is very desirable to steal since they are valuable and can easily be sold to receivers of stolen goods. The spontaneous stealing of screens and similar products in public premises is a growing problem. For example, nobody notices if a false service technician removes a projector in a public area and walks away with the projector. 
   There are many different alarm systems that prevent this type of theft. A common system is a cable, or another signal equipment, that is pulled through the equipment to be protected. An existing opening, such as at a fan, is often used where it is possible to insert the cable and pull out the cable to create a loop that triggers an alarm when cut. This type of alarm system has many drawbacks such as the loop may be attached to, for example, a plastic piece that may be broken or cut so that the equipment may be removed without cutting the loop and the alarm is not triggered. Further, this type of alarm may be by-passed by a conductor that takes over the function of the loop when the loop is cut so that the system senses the intact loop and the alarm is not triggered. 
   Other alarm systems exist such a metal plates that senses that the contact of the equipment is still connected to the wall or special devices that are mounted in the equipment to be protected. 
   Some systems sense the current that is delivered to the protected equipment and sends an alarm when this current is too low. One problem with these systems is that they do not function in case of a power outage. 
   SUMMARY OF THE INVENTION 
   The present invention relates to an arrangement and a method for detecting unauthorized removal of electronic equipment that solves the above-mentioned problems. The arrangement is arranged between a power source and the electronic equipment and includes a first current recognizing element. The detection of unauthorized removal is obtained by sensing a level of the current that flows to the electronic equipment. The arrangement of the present invention further sends a signal to the electronic equipment so that the signal is adapted to bounce back to the arrangement. The detection of unauthorized removal is obtained when the following conditions are met; the current sensed is lower than a predetermined value and the bounced back signal is absent. In this way, the advantage is obtained that the alarm will not be triggered in case of a power outage, when the current is thus zero, as long as the apparatus is connected and the bounced signal can be detected. 
   In a preferred embodiment, the arrangement has an alarm unit arranged to send an alarm signal to an alarm center when the detection of unauthorized removal is obtained. 
   In a further embodiment, the arrangement includes a second current recognizing element that senses the current delivered from the power source. In this embodiment, the bouncing signal is sent to the electronic equipment when the current sensed by a second current recognizing element is lower than a predetermined value. 
   In a preferred embodiment, the arrangement includes a unit that sends a signal to the electronic equipment. In case of power outage, the unit is transferred to operate via the batteries. In this way, the removal of the protected equipment is detected even during a power outage. The batteries are dimensioned to handle continuous operation for 24 h and the alarm for at least 5 h when there is a power outage. The lifetime of the batteries is about 5–6 years. When the battery level is reduced below a level, this is indicated so that the batteries can be replaced. During continuous normal operation the batteries are charged. 
   In a preferred embodiment, the arrangement further includes a unit that is connected to the audio-contact of the electronic equipment. The unit is arranged to sense a resistance that has a predetermined value and a signal is sent to an alarm unit when the resistance is different from this value. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  shows a preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   The present invention is now described in detail with reference to the attached figure. 
     FIG. 1  shows a block diagram of the preferred embodiment of the arrangement according to the present invention. The arrangement  1  is connected between the item that is desired to be protected  2  and the power source  3 . The arrangement includes a first current recognizing element  10  that senses the current that is delivered to the equipment. When the first current recognizing element  10  indicates that the level of current towards the equipments is lower than a predetermined value, that varies depending upon which equipment that is to be protected, a signal is sent to an alarm unit  11 . The alarm unit  11  is connected to an alarm center. When the alarm unit  11  alarms a signal is sent to the alarm center. The arrangement  1  also includes a second current recognizing element  13  that senses the current that is delivered from the power source  3 . When the second current recognizing element  13  indicates that the current is too low, a signal is triggered to the unit  14  that goes into a so called loop mode and sends a signal at a predefined frequency to the equipment  2 . This signal bounces back to the unit  14  when the protected equipment  2  is in place. In the case when the equipment  2  has been removed from its place, the signal sent by the unit  14  will not bounce back and the unit  14  sends a signal to the alarm unit  11  that sends out an alarm. The unit  14  is equipped with batteries for ensuring it functions during power outages. 
   The arrangement  1  also includes a unit  15  that is connected to an audio-contact of the equipment  2 . The unit  15  senses a resistance 75 Ohm and sends a signal to the alarm unit  11  when the resistance sensed is different from this value. 
   The invention is not limited to the above illustrative preferred embodiments and can be modified within the scope of the spirit of the invention as described in the appended patent claims.