Not much info to go on here. When my propane/carbon monoxide detector went off it was very evident when you were inside the coach. It also had a blinking light on it.
Depending on your coach, there are a number of things that can beep. Here is a list of things that have beeped in mine. All were easy to locate.
Propane/carbon monoxide detector
Smoke detector
Fridge (when on gas and no flame would start)
Tankless water heater control (when started but air in gas line)
Microwave when food was done
Just "use the force" to locate the beeping sound.