Heiman HS-720ES-M - Matter carbon monoxide detector with an electrochemical sensor, 85-dB alarm, and app notifications The Heiman HS-720ES-M is a smart carbon monoxide detector with an electrochemical sensor and modern Matter technology. The highly sensitive sensor continuously monitors the indoor air for carbon monoxide. If CO levels reach dangerous levels, a flashing red LED and the built-in alarm, which emits a sound of at least 85 dB at a distance of 3 m, will sound the alarm.