When the First Alert SA702CE optical smoke detector detects smoke, it produces an alarm with an audio signal of 85 decibels. You can't miss it. The smoke detector measures 8.5x8.5cm, so it's very compact and you won't have to deal with a bulky box hanging from your ceiling. Since the detector runs on 2 AAA batteries, you can mount it anywhere in the house. To be sure that it's still working, test the smoke detector every month using the test button. When you get a false alarm, press the pause button to stop the audio signal immediately.