The Fieldpiece RCM4 Replacement Carbon Monoxide (CO) Smart Sensor replaces the carbon monoxide sensor within the SCM4 or ACM4 CO Detectors. This sensor is field-replaceable for an easy user installation and comes pre-calibrated and certified for more accurate readings. The advanced three-pin sensor measures up to 1000 ppm carbon monoxide. The RCM4 is fast enough for walk-around tests and suitable for the home or office, automotive workshops, and underground carparks. The service life of the sensor is approximately 2 years and dependent upon exposure to contaminants in which repeated exposure will shorten the life.