The Alecto SA-49/1 consists of 4 smoke detectors with a time-out button each. This button is used to turn off the sound for 10 minutes. Thanks to this 4-pack, you'll have enough smoke detectors to secure your house in one go. The smoke detector detects slowly smoldering fires and emits an audio signal of 85 decibels when detected. Insert the 9V battery in the detector and install it anywhere in the house. Test the smoke detector regularly via the test button. That's how you make sure it's still working.