The ACM4 is a carbon monoxide detector (CO detector) accessory head for use with Fieldpiece modular instruments. It has a fast reacting electrochemical sesor specific designed to detect carbon Monoxide (CO). Use the ACM4 to hunt down sources of potentially life-threatening, poisonous gas. And easily replace the sensor in the field when necessary. Carbon monoxide (CO), a product of combustion is an oderless, colorless gas. Faulty combustion equipment is one source of this dangerious gas known as the "silent killer". The ACM4 carbom monoxide detector measures CO in parts per million (ppm). Use it for walk-around tests to help pinpoint sources of CO indoors.