Review on X-Sense SC08 10-Year Battery Smoke and Carbon Monoxide Detector with LCD Display, Dual Sensor Smoke and CO Alarm, UL 217 & UL 2034 Compliant, Auto-Check Technology by Tone Hatton

Glue the holder to the wall, mark three holes, drill, insert inserts, insert screws, then just glue the sensor and screw it on. It starts and checks itself automatically. If it lasts anywhere near 10 years I'll be happy. Tired of looking for the source of the warning sound and changing batteries. If you're placing it against a wall rather than a ceiling, you should orient it so the display is on top and not to one side. or another one that would look like crap. I've found that if you place the word "device" - from the printed sentence along the edge of the holder - just below when you install the holder, and then rotate the detector starting at about 10 o'clock, it will come up right out. If you don't have a 6mm drill bit, a 13/64 bit works well too. Or close, most likely.