The LOX R40Door Hold Open Magnets are operating on a fail-safe principle similar to common Electro Magnetic Locking Devices. Door Hold Open Magnets consist of a round electromagnetic lock and steel armature plate. Doors with Door Hold Open Magnets installed are usually required to remain in an open position for the general public or pedestrians and can be released by dropping the power to the device. The R40 Series devices are WALL mounted and come in 12VDCand 24VDC.