We have or had a burglar alarm on our coach. One of the reasons we bought the coach.It was installed by the Dealer we think. When they wrecked it they didn't reconnect it or something. the siren is still there along with regular horns in addition to the air horns.
Don't know but suspect if they force their way in there will be enough noise to draw everybody from the restaurant.
You didn't say if they used a key, or activated the remote door opener or broke in.
I'm not sure how universal our coach door keys are. Hopefully not as universal as bay door keys. There have been devices around to open electronic operated locks for some time.
It sound lie they were somewhat familiar with coaches, since the set the brake to operate the slide. Anone not familiar with a coach with slides might take them a while to figure it out or even find the switch to open the slides. We've parked at two or three Cracker Barrels with the coach to eat. Unfortunately it was a long way from the restaurant or even in another lot, in Fla. We try to have one of us at the coach at all times, at stops. She goes in the store. She comes back out and I go or something she may not have bought of something I want. This year the alarm will be fixed and I will talk to someone at the factory about the keyed lock.
Maybe it is time we stated taking Dakota with us.