Detector brackets can used for celing mounting to conceal cables inside. 

Detector brackets are they necessary?

A. The detector has a indented hole in the back, a built in spot to mount a screw on the wall and then put the detector on it and pull down.

The brackets are great if you wish for the detectors to go onto the ceiling and conceal the cables inside. We also sell a PK 3 that are swivel mounted, great for a corner of a room.