A clue this is happening is that a normal blue flame becomes yellow and smoky. A properly engine is essential to eliminate carbon monoxide hazards. Fuel that is contaminated, stale, or of the wrong octane number for the engine. Dirty or clogged flame arrester, malfunctioning automatic choke or faulty adjustment of manual choke plate, worn flat needle valve and seat, high float level, incorrect idle mixture adjustment, and dirty or worn injectors. Fully-integrated detectors will sound an alarm to any combination of carbon monoxide concentrations and exposure time that is hazardous to health.
Most alarm system combine both light and sound.
More sophisticated combine different colored lights with different alarm sounds. For example, one system responds with an amber warning light and an intermittent horn when unsafe levels of carbon monoxide accumulate, and a red light and continuous horn at dangerous levels of carbon monoxide. Some simple chemical carbon monoxide detectors respond with a color change of a sensor chemical in the presence of unsafe levels of carbon monoxide. These are not recommended in sleeping compartments. Boaters are unlikely to detect the presence of unsafe levels of carbon monoxide until there is a dangerous health hazard.