[Mike P]

If it helps, Mythbusters did a series of experiments to debunk the myth of disposable cigarette lighters spontaneously detonating in a car heated by the sun. Myth busted.

When I saw that episode I was a little surprised because over the years I've had three that were in pieces in the car when I got back in after work. No damage at all inside the car, even when I know I left one in a small door panel pocket.