The "touch FOB to the start button" uses RFID technology.
No power required on the FOB for that.
Go here:
http://en.wikipedia.org/wiki/RFID
Pay particular attention to the PASSIVE and also
AUTOMOTIVE technology. The Toyota implementation
is referenced directly.
I REEEEEALY wonder if active RFID is the only sustem
used in day to day SmartKey operation since there
are security issues.
It basically uses the power the
start button emits in the form of an RFID beacon and
echos back a reply encoded with it's unique ID. Each
FOB has a unique RFID associated with it.
I am NOT saying that day to day use of the FOB uses RFID.
It isn't nearly as secure as rolling codes but does work when
there is absolutely no power available onboard the FOB.