One word of caution against carbon monoxide detectors. The CO detector you buy at Home Depot will not show low levels of CO. You need to get one that is much more sensitive, usually one designed for a laboratory, they are usually well over $100 for a good one. The cheap ones will only show levels once they reach toxic concentrations. You want a low level CO detector like this one:
https://www.amazon.com/Kidde-KN-COU-...xide+low+level
With a cheap one from Home Depot you will actually feel the effects of toxic CO before the detector goes off, don't be fooled!!