Smoke detector

Many alarms are fitted on the ceiling/wall between the kitchen and the habitation door. Velcro would be suitable so that you don't have to screw into the ceiling. 

It would be best to follow the instructions on the box of the unit 

In both our caravans they were by the door. In our MH they are at the bedroom end of the van.

In our last Barcelona, both were fitted near the door and the toaster always set the smoke detector off. In our present Knaus, they are attached to the roof, between the fixed single beds and some way from the kitchen worktop and we have never had that problem.