made to open the door 100 note that in fig5 balls 27 have been pushed into engagement with groove 26 of pin thus providing mechanical resistance to separation of armature and electromagnets referring again to fig1 when the electromagnets deactivated there is no attraction between the armature 2 and the electromagnets 1 thus if an attempt it made to open the door the armature easily separates from the electromagnets pin 24 is free to release from sleeve 42 as balls 27 are not held in engagement with groove 26 by shoulder 41 referring to fig7 a an alternative embodiment of the invention is shown in this version two microswitches 238 239 are used the microswitches are actuated by the heads of actuation screws 240 241 the depth of insertion of each of screws 241 240 into plate 224 dictates the force required to actuate either of microswitches 239 240 referring to fig7 b a moderate force is being applied to device 200 which is comparable to the force that might be applied by a person attempting to push open a door the force is balanced by compression of spring 230 it can be seen that microswitch 239 has become actuated by the head of actuation screw 241 referring to fig7 c a large force is being applied to device 200 which is comparable to the force that might be applied by a person attempting to force open a door the force is balanced by further compression of spring 230 it can be seen that.