A mechanism for an electro-mechanical lock. The mechanism comprises a shackle or strike moveable in a bore. A cam is rotatable between a first cam position in which movement of the shackle or strike in the bore is prevented and a second cam position in which movement of the shackle or strike in the bore is not prevented. A blocking pin is moveable between a first pin position in which rotation of the cam is prevented and a second position in which rotation of the cam is not prevented. A solenoid has a plunger having a stable extended position in which movement of the blocking pin is prevented and a stable retracted position in which movement of the blocking pin is not prevented.