The Chacon LB34233 (5 years) is an optical smoke detector. The included battery has a lifespan of 5years, so you won't have to replace it for a while. When the battery is almost empty, it'll make a sound. You'll immediately know that it's time to replace the battery. When the sensor detects smoke, the smoke detector will produce an audio signal of 85dB. To make sure the smoke detector works, you can press the test button once a month. The detector will go into test mode, and you can be sure it works when you really need it.