Chem-optical technology alarms are also known as gel cell or biomimetic technology alarms. These alarms utilize a type of sensor that mimics the response of hemoglobin, in the blood, to carbon monoxide. Alarms using this kind of sensor are usually battery powered.
One main drawback that remains is that the sensor can non-reversibly accumulate carbon monoxide and other contaminants over time, which can eventually lead to false and/or nusiance alarms. Some chem-optical (gel cell) alarms on the market today contain an expensive relacement battery and/or sensor, which must be replaced periodically.