Just about any ultrahigh-frequency (UHF) system could be set up to cover a room. Passive UHF readers could be set up around the room, and could start and stop reading as directed. However, there would be no way, using a conventional UHF system, to determine precisely where someone was located within a room. You could not, for instance, divide the room into four quadrants and know for certain that a person was in one quadrant and not another, if people were standing near the border of two quadrants.
Mojix offers a phased-array antenna that allows a user to more precisely locate tags within three dimensions (see Mojix Takes Passive UHF RFID to a New Level). The system is accurate to within 3 feet, so if you needed to precisely know that a person was on one side of a line or another, that would not work. If you were willing to utilize an active system, you could try ultra-wideband (UWB) technology, which can locate tags to within a few centimeters.
—Mark Roberti, Founder and Editor, RFID Journal
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