The UL-listed SECO-LARM U.S.A. Electromagnetic Door Holders are designed for virtually any remote door release application whether residential or commercial. Fail-safe operation, tri-volt coils, and an adjustable armature plate allows for easy and flexible installation. The door holders come in two mounting styles: surface-mount (DH-151SQ) and flush-mount (DH-171SQ). The adjustable armature plate reduces the installation time, adjusts to door alignment changes, and has a low-profile design. Doors are held securely with a holding force of 35 lb. and when released there is no residual magnetism. The door holders have built-in voltage spike suppressors and support three voltages: 12/24 VAC/VDC, and 120VAC.