I tried an experiment just now, to see if I could leave my car powered on but not started while I tried to communicate with it. The $23 Bluetooth adapter with a 100 meter range is still coming, but I wanted to know how safe it was going to be. 1) The car will go from on (single push of Power button) to Ready (push Power with foot on brake) even if the fob was walked into the house after turning it on. All you get is a dashboard warning that the key/fob is missing. 2) The locking buttons on the doors seems to be related to Smart Entry, and didn't work when I wasn't carrying the fob. Never having seen another Prius up close, if all of them have buttons and they all work, I don't know what the problem was other than lack of fob...
