Kidde KN-COB-IC Hardwire Carbon Monoxide Alarm with Battery Backup, Interconnectable (4 Pack) Battery pull tab eliminates battery installation time and keeps battery fresh Quick connect installs quickly with snap on harness Adjustable mounting bracket allows for fast installation and perfect alignment Tamper resist locking feature to deter battery and alarm 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