carbon monoxide detector

This is why I hate combination detectors - can't tell which "side" has activated or is at fault... As others stated, it is often the PROPANE side that alarms from various sprays, since the propellant is often a butane base (cousin of propane). The hard-wired CO detectors do tend to alarm under a low-voltage issue. I like your idea of a separate CO detector - I have a battery-powered Kidde unit that has an LCD display showing actual PPM readings of CO - that way I know if I have an issue or not. CO can also originate from an outside source - nearby exhaust from an adjacent engine/generator/etc. If it activates, it doesn't mean it's an error - no other way to detect CO, so I like the redundancy of 2 units. At least with propane, in the event of a gas leak, the second detector is noses - at least you can smell propane! ST