You are probably thinking of piezoelectric pickups. Same principle but think of grill/gas ignitors: https://en.m.wikipedia.org/wiki/Piezo_ignition https://en.m.

You are probably thinking of piezoelectric pickups. Same principle but think of grill/gas ignitors: https://en.m.wikipedia.org/wiki/Piezo_ignition https://en.m.wikipedia.org/wiki/Piezo_ignition