There was some discussion threads back from late June or early July that discussed these quite a bit. To summarize, there are different systems being offered by dealers depending on location. Basically they all work the same way, beeping more frequently until steady tone as you get closer to an object. It's not foolproof, low objects, poles or slanted surfaces may not reflect the sound waves back to trigger it. My system had the nice option of having the tone integrated with the car audio, others reported having a separate beeper installed somewhere near the rear window or deck. You have the option of using color coded or black sensors depending on device model and color of car. After 3+ months having this system, I remain satisfied. I haven't backed into anything yet!

Two climate control systems, one inside and the other at the tailpipe.

2007 Camry Hybrid (in service June 2006)
FE: 6.77L/100km (34.8 mpg) over 37750km (23450mi)
75% city - Ave trip 20 min - 2 Winters