Philv, my carbon monoxide was mounted above bed just like yours and I had to replace. I replaced mine with a Kidde CO/gas detector from Lowe's that plugs into an outlet, has a battery back up and an LED with the parts per million readout so you can see why it is alarming. CO detectors can be mounted anywhere as the gas readily mixes with the ambient air. Gas however lays low and that is why I picked an outlet near the floor. So now I have 2 LP gas detectors. Good luck and keep up posted on results.
2012 F350 Lariat CC SRW 6.7L Powerstroke