Kidde KN-COB-LCB-A Tamper Resistant Plug-In Carbon Monoxide Alarm with Battery Backup, 6-Pack 9-Volt battery backup provides continuous protection Loud 85db alerts you of deadly CO gas Includes tamper-resistant feature The low battery hush silences low battery chirp warning up to 12-hours to maintain protection 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