Why is one carbon monoxide detector going off but not the other?

When only a single carbon monoxide detector in your home sounds its alarm while other units remain silent, it typically indicates a localized chemical exposure, a dying battery warning, an expired sensor on that specific unit, or wireless communication interference rather than a whole-house gas leak. Because carbon monoxide mixes evenly throughout indoor air, a true gas leak would normally trigger all detectors. A single unit sounding may be reacting to nearby aerosol sprays, cleaning products, or localized sensor degradation. You can troubleshoot alarm safety by treating every alert as a potential hazard. You can verify that your corrective action is successful when evacuating immediately, calling emergency services, and having professionals test the air ensures whether the single alarm was reacting to a localized issue or a true leak.