If the propane detector in your RV sounds even though you’re sure there is no leak it could be defective but most likely it is just a low battery.
Your RV’s propane detector is powered by the coach battery. If the voltage in the battery is too low the detector will sound.
Fully charge the battery. If the detector sounds you may have a defective unit but have it checked by an RV shop before you replace it.
If the Detector sounds when the propane is on the you have to get an RV shop to check the entire system for leaks.
One other possibility, the detector can be set off by different sprays such a hairspray and deodorants. Often times these and other spays use propane as the propellant.