There are many dangers that you want to protect your home and family from. This 4-in-1 Smoke & Fire, Carbon Monoxide & Natural Gas Alarm is the first and only alarm that protects you against all four of those dangers. The IoPhic sensor responds 87% faster to slow smoldering fires and is also the quickest sensor to respond to fast flaming fires. You can trust this alarm thanks to the microprocessor intelligence that virtually eliminates nuisance alarms through auto sensitivity calibration and ambient condition compensation. The 120 Volt AC hardwired alarm is interconnectable with up to 24 USI or Universal brand devices using existing wiring and mounting. It features a 9 Volt battery backup. USI (Universal Security Instruments, Inc.) makes the most innovative home protection solutions available today. Saving lives is what we do for a living.