From the sounds of things it is an intruder alarm.. I know of no RV that has these standard so it will be after market.. and this means that the only way to reset it is to do one of the following:
1: Contact the Previous Owner and ask
2: Locate and identify the unit, contact the manufacturer or, more likely, visit their web page and download the owners' manual for the device.
NOTE: if there is a keypad with a code.. the "Default" code is often set to one of the following
0 0 0 0 and 1 2 3 4