The digital readout of the Kidde Plug-In Digital Carbon Monoxide Alarm with 9-Volt Backup continuously displays carbon monoxide levels from 30 to 999 parts per million (PPM) and will sound an 85dB alarm when dangerous levels are reached. The carbon monoxide level sensed is continuously displayed and updated every 15-seconds and the peak level memory shows the highest level of carbon monoxide present since the last time the unit was reset or unplugged. Protection continues during power outages thanks to a 9-Volt battery backup. Plug-in carbon monoxide detector with digital readout. 85dB alarm sounds when carbon monoxide reaches dangerous levels so you can protect your family. Test/reset button to check for proper operation and reset the unit. 9-Volt battery backup provides protection during power outages. Displays carbon monoxide levels from 30 to 999 PPM. Updates digital reading every 15-seconds. Peak level memory displays highest carbon monoxide level recorded since previous reset or unplugging. Plugs into AC receptacles. Carbon monoxide detector utilizes an electrochemical sensor to detect fire hazards and sounds an 85 db alarm when a hazard is detected. *Check with your state and local fire and Building/Safety codes for specific information regarding smoke & Carbon Monoxide Alarms.