If you simply wanted to monitor workers entering and leaving a particular room via one or more doorways, you could set up a high-frequency (HF) system in which each employee would wave a badge near an RFID reader. If you needed to collect data automatically, you could use an ultrahigh-frequency (UHF) portal reader. Keep in mind that water absorbs RF energy in the UHF spectrum, and that makes it difficult at times to read a tag close to a human body. This can be overcome by placing the tag on part of the uniform that is not close to the body, such as a hat.
Alanco Technologies offers a system known as TSI Prism. This active RFID solution can monitor inmates and guards in real time. Prisons in L.A. County and Missouri are already employing the technology (see L.A. County Jail to Track Inmates and Alanco to Outfit Additional Missouri Corrections Facilities With RFID).
—Mark Roberti, Founder and Editor, RFID Journal