The Ei208i series carbon monoxide detectors have an electrochemical sensor to measure CO concentration in the air. For maximum accuracy, each sensor is individually calibrated and tested in CO gas. Every 4 seconds the sensor checks the CO concentration in the air. The carbon monoxide detector triggers an alarm as soon as a CO concentration greater than 43 ppm is measured. With the new, integrated AudioLINK technology you are always up to date. The smartphone makes it child's play to receive important data, such as operating time and battery status, clearly presented.