Tamper resist feature unit goes into constant alarm mode if it has been unplugged or has come loose from the outlet * 9V Battery backup provides continuous protection even during power outages * Test/Reset button tests the unit for proper operation and resets the Carbon Monoxide alarm * 7-Year end of life warning alerts user to replace CO alarm after 7-years of operation (40% longer than other CO alarms) * Kidde?s carbon monoxide alarms meet the requirements of Underwriters Laboratories (UL), an independent facility that tests products for compliance with widely-accepted safety standards