Defeating Electromagnetic Door Locks

Electromagnetic locks on the doors to keep them locked while the clerk is occupied
cleaning the store at night so robbers can't ambush him while he's out from behind
the bulletproof glass. These locks have around a 1,500 pound hold strength so it's
impossible to force them open manually.

But you can open them from inside easily without the clerk having to buzz you out
because there's a circuit that detects when a person touches the exit bar that de-
energizes the electromagnet. This is a simple touch sensitive circuit that detects a
change in capacitance when a conductive body (like yours) drains it.