There are three types of carbon monoxide detectors: a biomimeticsensor, a metal oxide semiconductor, and an electrochemical sensor. A biomimetic sensor contains a gel that changes color when it absorbs carbon monoxide. When the gel changes color it triggers an alarm to go off. A metal oxide semiconductor detector has a silica chip with circuitry that lowers its electrical resistance when it detects carbon monoxide, triggering an alarm. Finally, an electrochemical sensor has electrodes immersed in a chemical solution that senses change in electrical current when carbon monoxide is present, which triggers the alarm.