Here`s the link for todays MiceAge article. Privacy at WDW Waning? RFID and Tracking UpdateMiceChat .
Apparently the wristbands are not as passive as advertised. Batteries were found in them , and similar devices have a range of 30 feet. Park visiters were offered ride photos in emails on rides that they didn`t use the wristband for FP+. There is speculation that you can be tracked throughout your visit. I like the line about tracking the time between you buying a burritto and using the bathroom , and how long you were in there.