CO detector

The devices ... can either be battery-operated or AC powered (with or without a battery backup). Battery lifetimes have been increasing as the technology has developed and certain battery powered devices now advertise a battery lifetime of over 6 years. Some smoke detectors are equipped with an internal rechargeable battery backup that recharges when the detector is receiving AC power. All CO detectors have "test" buttons like smoke detectors. CO detectors can be placed near the ceiling or near the floor because CO is very close to the same density as air. ... CO detectors are available as stand-alone models or system-connected, monitored devices. System-connected detectors, which can be wired to either a security or fire panel, are monitored by a central station. In case the residence is empty, the residents are sleeping or occupants are already suffering from the effects of CO, the central station can be alerted to the high concentrations of CO gas and can send the proper authorities to investigate. The gas sensors in CO alarms have a limited and indeterminable life span, typically two to five years. The test button on a CO alarm only tests the battery and circuitry, not the sensor. CO alarms should be tested with an external source of calibrated test gas, as recommended by the latest version of NFPA 720. [Carbon monoxide detector. Wikipedia]