Put smoke detectors in their place and keep them there with this durable bracket. It conveniently adjusts to fit 1/4" to 1-1/2" wall or ceiling thickness. Plus the bracket doubles as a template so you get perfect cutouts every time! 
Arlington™ Round Low-Voltage Mounting Bracket for Smoke Detectors
Put smoke detectors in their place and keep them there with this durable bracket. It conveniently adjusts to fit 1/4" to 1-1/2" wall or ceiling thickness. Plus the bracket doubles as a template so you get perfect cutouts every time!