Many Newells have an alarm system built in at the factory. On mine, it is only attached to the door and the bay door that houses the control box. There is also a panic switch in the bedroom.
If your coach doesn't have an alarm or you want to expand to a more sophisticated alarm, most automotive alarm systems can be installed in a Newell. Some custom auto stereo businesses will install them or you can do it yourself if you are good at it. You can get some very sophisticated systems these days including ones that will signal the remote that it has been set off if it is in range.
I would NOT put a motion sensor on a coach. Winds are too likely to set it off. Take a look at the Viper 5902
Responder HD Color SuperCode SST 2-Way Security and Remote Start System.