The answer to 'when to replace carbon monoxide detector' is that carbon monoxide detectors should be replaced every 5-7 years, or sooner if the manufacturer recommends it. Carbon monoxide detectors have a limited lifespan and can become less effective over time, so it's important to replace them regularly to ensure your home's safety.
Most carbon monoxide detectors have a lifespan of 5-7 years, after which the sensors can start to degrade and become less sensitive to detecting dangerous levels of carbon monoxide. The exact lifespan can vary depending on the detector model and usage, so it's a good idea to check the manufacturer's recommendations and replace the detector accordingly.