Kidde KN-COP-IC Hardwire Carbon Monoxide Alarm with Battery Backup and Digital Display, Interconnectable 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 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