There are three different types of carbon monoxide detectors for residences and businesses: metal oxide semi-conductor (MOS), biometric, and electrochemical. Each of them work in different ways but for the most part the use different chemicals that react to CO gas that then set off an alarm.
The MOS was the original technology for detecting carbon monoxide (CO). Heated tin oxide reacts with CO to determine the levels of the toxic gas. But the unit must be connected to house power in order to work.
If the power fails the unit usually has a battery back up that last for 20 hours. However, if power is still out and someone turns on a space heater the unit becomes useless.
In a biometric detector gel-coated discs darken in the presence of CO and the color change sounds an alarm. This technology is far less expensive and can be battery operated however the batteries need to be checked regularly to ensure safety.
Electrochemical detectors work when a chemical reaction with CO causes an electrical current, setting off the alarm. The unit is highly sensitive and offers the most accurate readings of all CO levels. These high end units come with a continuous digital readout and sometimes a memory feature that allows you to check past CO levels. A fast reset time and an alert when the sensors need replacing are some of the other features.
Carbon monoxide detectors can be purchased at most hardware stores and all three of these detectors have been repeatedly tested to provide the proper protection. However, a difference in price may be seen in the number of features and how the unit is set up.
It is also important to know where to set up a carbon monoxide detector before purchasing a unit, as some require additional wiring and others just need batteries.