Peter
I don't quite understand what you are saying.
If I were you I would be less concerned about somebody using the device without permission, and more concerned about somebody stealing the hardware.
I don't quite see the difference between "using without permission" and stealing.
If they steal the device I hope they try to "use it without permission" and by doing so they tell me where the device is. Doing the telling without permission would be very easy to hack.
How would you advice to avoid nicking a lawnmower robot?
Best regards
Jantje