The relase mechanism of an electronic timelock employs two bistable electromagnetic actuators 1 and 2 to control the "on-guard" and "off-guard" conditions of the lock, each actuator comprising an element 4 of ferro-magnetic material whose magnetic polarity serves as the "memory" of whether the lock is in an on- or off-guard period and which polarity is reversed by single magnetising pulses through the associated coils 3 when each successive on-and off-guard period is programmed to commence. More particularly, when on-guard the coils 3 are pulsed in one direction to magnetise the elements 4 so that they are attracted by poles P1 of the field magnets 5. In this condition they block a beam 10 which is pinned at 11 to a bolt 8 which in turn blocks a bar 6 which is attached to the door's boltwork. When off-guard the coils 3 are pulsed in the opposite direction to reverse the magnetisation of elements 4 so that they are attracted by poles P2 of the magnets 5. This enables the beam 10 to be lifted with the bolt 8 as a spring snib 12 on the bolt rides up a notch 19 in the bar 6 when the latter is retracted. If the bar6 isforced when the mechanism is locked the snib 19 is turned until a face 20 on the bar is blocked by the bolt 8, thus limiting the upward force which can be applied through the beam 10 to the elements 4. If one actuator should for any reason fail in the on-guard position the lock can still be released when the other actuator switches to the off-guard position, by pivotal movement of the beam 10.