I've got a variety of heaters from a calor heater, bio ethanol fireplace to a old school gas parabolic heater and a few in-between.
I've got 2x CO alarms in the house already if I was to use a gas heater inside a co alarm would migrate into the room we would use ideally the one that displays the ppm of CO . Enabling us to deal with a potential issue before any problems developed..
Both units are kiddie.
Know from sitting the British standards examination for work about ventilation and co alarm placement (as per the instructions) one says place at head hight the other just under 150 mm from the ceiling so it pays to read the booklet
Homes and Retreats