Just to be clear because I don't want anyone to read this and take it as fact...

Smoke detectors detect smoke by looking for particles.

Some devices are combo Smoke/Carbon Monoxide (CO) detectors. They cost more but it's good to have both and it's easier to have fewer devices.

You can also get stand alone Carbon Monoxide detectors and absolutely should. It's odorlesss and very deadly and is produced by burning gas/oil/propane or whatever else you burn to heat your house.