Kidde 21006407 AC Hardwired Operated Digital Display KN-COP-IC Carbon Monoxide Alarm, 120V Digital display displays the level of carbon monoxide the unit is sensing Battery pull tab eliminates battery installation time and keeps battery fresh Peak level memory displays the highest CO concentration measured since the last reset Tamper resist locking pin helps deter alarm tampering and theft Kiddes carbon monoxide alarms meet the requirements of Underwriters Laboratories (UL), an independent facility that tests products for compliance with widely-accepted safety standards