Mister_e,

I also thought to use the + wire from the ignition key lock but
it would not be so easy to get it and it's not always located
at the same place.
I thought it should be something like a mercury switch or a
metal ball etc.
Let's say if you push the car it should be already enough to switch
on.
My project is a gps data recorder and the switch will avoid the pic
to stay on.

Bye
Lotondo