USI Natural Gas Alarms are capable of detecting both natural gas (methane) as well as carbon monoxide. Available as 120v plug-in natural gas alarms or hardwired natural gas detectors, USI Methane Detectors offer versatile installation options backed by reliable technology. USI Hardwired Natural Gas Alarms come with the added ability to sense multiple threats. A 4-in-1 Hardwired Natural Gas Alarm will detect both types of fires (smoldering and flaming) as well as carbon monoxide. A 2-in-1 Hardwired Methane Alarm will detect the presence of natural gasses and co. Plug-In methane alarms provide the very same protection, but offer more versatility when it comes to installation due to their easy to setup. Simply plug into any outlet (no additional wiring is required).