Energy efficient multi-stable lock cylinder

Some embodiments include a lock cylinder comprising: a plug assembly having a front portion and a back portion; a housing shell within which the plug assembly is rotatably disposed, wherein the housing shell includes a notch; wherein the back portion of the plug assembly comprises: a locking pin that is movably disposed, and wherein the locking pin is configured to prevent a rotation of the plug assembly when the locking pin is engaged in the notch and prevented from retracting by a multi-stable mechanism; and the multi-stable mechanism having at least two stable configurations corresponding to respectively to a locked state and an unlocked state, wherein the multi-stable mechanism can maintain the stable configurations without consuming energy; wherein, at a first stable configuration, the multi-stable mechanism prevents the locking pin from retracting, and, at a second stable configuration, the multi-stable mechanism enables the locking pin to retract.