Nighthawk Plug-In Carbon Monoxide Alarm with Battery Backup and Digital Display with Fire Sentry Compact Smoke and Fire Alarm, Ionization Sensor, Battery-Operated Value Pack. * 9V Batteries Included, Two Protections from Deadly Threats in one great value Pack. * Displays level of carbon monoxide the unit is sensing. * Three Convenient mounting options. Battery backup provides protection during power outages. * Alarms meet requirements of Underwriters Labs (UL), compliance with widely-accepted safety standards.