Kidde Carbon Monoxide (KN-COB-B) and Smoke Alarm (0916) Value Pack CO2 alarm uses three AA batteries, included Smoke alarm uses one 9V carbon zinc battery, included CO Alarm snap open cover gives immediate access to batteries Smoke alarm hush feature Kiddes smoke alarms and carbon monoxide detectors meet the requirements of Underwriters Laboratories (UL), an independent facility that tests products for compliance with widely-accepted safety standards