Patent ID: 7342497

Claim:
A system for monitoring objects having an RFID device associated therewith that are in a defined space, said system comprising: a plurality of RFID devices associated with respective objects, wherein at least ones of the objects and their associated RFID devices are within the space at least for a period of time, each RFID device comprising: a memory having stored therein unique identifying information and codes representing at least two different transmitter power levels; an antenna for transmitting and/or receiving electromagnetic signals; a modulator coupled to said memory for modulating the unique identifying information and the transmitter power level codes stored in said memory; and a transmitter coupled to said modulator and to said antenna for transmitting at least two messages via said antenna, wherein each of the at least two messages includes the modulated unique identifying information and a modulated different one of the transmitter power level codes, wherein the power level of said transmitter is controlled responsive to the power level code to correspond to the power level represented by the power level code in each transmitted message when each message is transmitted; whereby the transmitter power level changes to correspond to the power level code contained in each of the at least two messages transmitted; a plurality of relay devices arrayed in said space, each said relay device including a receiver for receiving the messages transmitted by said plurality of RFID devices and a transmitter for relaying the messages received from said RFID devices; and a processor for receiving the messages relayed by said plurality of relay devices and for processing the information therein, wherein said processor decodes the unique identifying information and the power level code from each relayed received message for associating the received messages from each RFID device and the power level thereof, said processor selecting the received messages from a particular RFID device at the lowest power level that produces at least two corresponding received messages relayed by ones of said plurality of relay devices for determining the location of that particular RFID device in the space, whereby the RFID device and its associated object are monitored.