Edwards 1505-AQN5 Door Holder is a high-quality device for use with single doors. The electromagnet assembly is a design for flush wall mounting.
The electromagnet is designed to be flush wall mounted inside a standard single gang outlet box. Field wiring connections are made to the electromagnet inside the electrical box. The catch plate assembly may be mounted to the door either by through-bolting. Or by using the concealed surface mounting plates.

Edwards 1505-AQN5 Door Holder is to be used on self-closing, swinging doors to automatically isolate an area when activated by a fire alarm, smoke detection, or also sprinkler system. Can also be operated by manual control — wherever the instant closing of doors is necessitated for safety. Or also for convenience.  So, in other words can be used in, Hospitals — for stairwell doors, room doors, long corridors, and schools — exit doors (closes all doors at once by pushbutton control). Also in offices (instant privacy by pushing a button on your desk), nursing homes, and public buildings. The 1505 Series door holder is an auxiliary device designed for wall mount applications that require holding single doors.