A friend of mine had the same problem
I installed one of these, its self powered, and arms as soon as you take the bluetooth key away
took a bit of thinking about but it works
oddly the last time it chirped the tractor had been moved about 6 feet in the dutch barn, almost as if some one was planning to come back for it
The smart tracker for motorcycles
monimoto.com
if you have a building with power and wifi nearby then a small camera would also be useful as it will indicate movement
PM me if you need some help