The Alecto SA-102 Mini will alert you when it detects smoke. The package consists of 2 smoke detectors. The loud, 85-decibel audio signal means you don't have to worry you won't hear the alarm. The smoke detectors each run on 3 3V batteries, so you can put them up anywhere in your home. Since the smoke detectors aren't very big, they're not an eye sore. The test button helps you check if the smoke detector still works. That's always good to know.