One of our smoke alarms quit working, and it was just a little more for this twin-pack than it was for just one. After seeing just how easy putting in the battery was (no taking the smoke alarm off the ceiling--yippee!), we decided to replace another of our older alarms with the spare. On top of the ease of battery replacement, the screw-holes on these new First Alerts line up perfectly with the original smoke-alarm bracket, so putting them in was a five-minute job.

Easy to install. May have to drill holes or use alternative method to attach. Uses batteries so eventually will need replaced. Have one in kitchen, not good, goes off very easily with very minimal smoke from cooking. Had to disable it twice, will probably move it