Carbon Monoxide (CO) plug-in detectors have a limited lifespan – 10 years and some are fewer than five years if you purchased your detector somewhere else. Many people think they can just plug in their CO detector and forget it. What`s important is that all detectors eventually lose their sensory capabilities and must be replaced. If your CO detector is up there in age, it`s best to replace it. You can also test the detector using a CO test kit available at many retailers.”