This electro-mechanical switch has four wires. Two wires (red & black) are the leads for the blue solenoid coil. When energized the latch catchment will release the silver hasp. See the two photos showing the unlatched and latched positions.The second set of wires (yellow & blue) are soldered to a micro-switch. The micro-switch lever is actuated when the lock is latched or unlatched. The other two photos show the resistance reading between the terminals of the micro-switch. When the lock is latched, the switch is closed and the resistance is low. When the lock is unlatched the switch is opened and the resistance is infinite.The integrated micro-switch allows you to determine if the lock hasp has actually moved after the solenoid was energized. For example, if the lock is holding a locker door closed until the solenoid is energized, the micro switch will indicate if some has opened the unlocked door. The micro-switch can also be used to determine if the lock hasp has been pushed back into the lock mechanism. In the locker door example above, the micro-switch can be used to determine if the locker door has been closed after the contents have been removed.The lock does have a mechanical safety release. The tongue of the solenoid shaft has a hole in it's tip. The silver shaft attached to the gray lock catchment passes through this hole. When the solenoid is energized. the tongue moves out from the blue solenoid coil. This movement causes the silver shaft to move, rotating around the pivot point in the gray latch catchment. You can manually release the lock by moving the silver shaft.The lock is solidly built. The case, lock catchment and solenoid frame are all metal. The micro-switch case is plastic but the lever arm is metal. The silver lock hasp looks sturdy enough. I have not integrated the lock into my project yet. I expect that it will work great in the design I am implementing.