The LOX R40PCH Door 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 R40PCH Series devices are WALL mounted with extensions and come in 12VDC and 24VDC.