What make and year rig do you have? First I would make sure that there are no LP leaks. Also make sure the battery disconnect switch wasn't engaged and your coach batteries are charged. Every time our rig is serviced they turn off the batteries and we have to reset the LP detector. There is a reset button on the detector. There are no batteries for the LP detector.
We have a separate LP detector that is not the CO2 detector. Our CO2 detector did start sounding for no reason in our 2004 class A. I found out online that they start doing that when they are going bad. We replaced the CO2 detector.