Computer theft is on the rise.  Presently there is no adequate deterrent to the theft of or access to electronic devices or systems.  Passwords are currently used to prevent unwanted access to the equipment, but information on how to clear passwords is available without security checks.  Thieves can easily erase the password and use the machine as if they were the owner.  Furthermore, passwords do little to actually prevent the item from being stolen at the time and place of the potential theft, when prevention would be the most effective.  It would be desirable to provide a method of securing an easily stolen electronic device by using (RFID) Radio Frequency Identification.  While preventing unauthorized use or theft, RFID allows the owner to disarm the security system and use the equipment by bringing a pocket item containing an RFID tag within range of the device.  The proper RFID tag would disarm the security system that would otherwise activate a visual or audible warning to deter potential thieves and/or render the device useless. 
A related need is as follows.  Energy saving devices are common in today's office.  One such device is the screen saver and auto powerdown programs on computers.  The computer displays a screen saver after a certain time of inactivity no matter whether the user wants to use it or not.  The proposed device would wait some specified time and then check whether the user is nearby.  It would turn off the screen only if the user wasn't present.  The ultimate system would also check at intervals to notice if the user had returned so the system or monitor could turn back on.  Integrated with a time function, the rules would be programmable to power down the whole computer if the user wasn't present after a certain time and then come on again in the morning when the user returned.  Any tampering while the owner was not present at night would result in a more severe reaction than in the daytime. 
Another version would allow secure printing of documents only when the originator was near the printer.  In the print driver that is displayed when the document is submitted for printing, the user would specify secure delivery.  The printer would hold the job in memory and begin "listening" for an RFID response from the matching user.  When the user arrived near the printer, the transponder would cause the printer to output (release) their prints when they arrived.  If more than one user is present, a confirmation would or could be required.  The same information about the presence of one or more authorized users would cause the printer to enter or exit a power saver mode. 
Notification and alarm systems are well known in the prior art.  For example, U.S. Pat.  No. , 305,055, assigned to the same assignee as the present invention, discloses a system of notification to selected remote stations in response to the detection of predetermined machine conditions.  Also, U.S. Pat.  No.  4,224,613 discloses a warning system that provides an acoustic warning whenever predetermined machine running conditions are exceeded. 
It would be desirable, however, to provide a computer theft and unauthorized usage deterrent that is effective, relatively simple to implement, and related to normal operator activity/presence, rather than implied time factors or a special disarming signal by the user. 
It is an object of the present invention, therefore, to provide a portable electronic device that can be used to control a wide variety of deterrent functions.  It is another object of the present invention to provide a small RFID tag that allows the use of a particular machine (or group of machines) when one or more authorized users are within a specified range of the machine.  It is still another object of the present invention to provide appropriate warnings, alarms, or system shutdowns whenever a device is moved or accessed without a suitable RFID tag within machine range.  Further advantages of the present invention will become apparent as the following description proceeds, and the features characterizing the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.