The Smartwares RM149 will sound the alarm when it detects smoke. This package consists of 4 smoke detectors for 4 times as much security in your home. The 85-decibel audio signal will get your attention immediately. The smoke detector runs on a 9V battery, which lasts about a year and is then easily replaced. Since the smoke detector runs on a battery, you can place it anywhere along the ceiling: no technical installation necessary. When the battery is empty, the smoke detector will let you know by emitting a beep.