It depends on the sensor. It's a new frontier, and there are limited standards for operation. Once they are woken up the first time (by rotation, a magnet, etc.), I believe many remain on. One guy over on the Toyota board actually placed 4 sensors in a home-made pressure bomb and kept it under his front seat to keep his light off!They don't broadcast a signal until they are rotating supposedly to save battery.. so I think they would appear dormant.
Sienna.. Turn on car.. push and hold button tpms .. wait a bit.. done.. i think..
Tx for your feedback.
Sienna: Hold the button until you see 3 flashes in 6 seconds. System becomes active within 60 minutes of the reset.
You are welcome!