I have posted about this subject before. I was going to buy new smoke detectors and after the wife vetoed that Idea and told me to get the combination units I found these.
Wireless Smoke and Carbon Monoxide Detector
There were some differences of opinion about the need but for someone like me that sleeps without their hearing aids I am not sure that I would hear a smoke detector going off in the living area when i have the door closed and the heat pump going. I purchased 4 of these One for the living area, one for the bedroom area, one for the underneath compartments and one for the electrical connection apartment. I did not get one for the engine compartment because I did not think there was as much danger from it when you are just sitting camped at night and while operating I worry about smoke from the engine itself being enough to set it off.
These are crosslinked and when one alarm goes off they all sound the alarm and tell you which alarm activated. This is by far the best price I have ever seen these.
Just as a disclaimer i have no connection to this product or this company. I use the linked smoke detectors in my rental houses for safety but I really do not remember if they are the same brand.