We sadly said goodbye to our old car, which was older than some of my students. And it had a cigarette lighter. These days you call it a 12V socket, apparently. I'd never used the cigarette lighter but in the interests of Physics... You push it in to connect the circuit. There is a spiral of resistance wire inside which gets red hot due to the current flowing through it, hot enough to light a cigarette. Then the lighter pops back out of the socket. My speculation is that the metal expands as it heats up and loosens the spring's grip, letting the lighter pop back up. I'll need to check that, though.
