Ionization, Carbon Monoxide and Natural Gas Alarm. 120V hardwiared with battery back up. Smart Alarm uses a single sensor to detect both CO and Natural Gas. Microprocessor Intelligence provides superior nuisance alarm resistance, temperature and humidity compensation, self diagnostics and Quick Find alarm origination features. Perfect for new or replacement installations, this hardwired 120 Volt AC/DC combination smoke and fire, carbon monoxide and natural gas alarm offers time-saving installation features, value and quality.