Hi Terry
There is such a product, and very widely used on Caravans these days. Its called the Sure Track MT2, no specialist installation required (no wiring and a 3 year self-powered battery). It does also reduce Insurance Premiums. They have Sold Secure Gold status too so with Caravan Club and other insurers it will reduce your insurance. Its a great little thing.
I became aware of them at the Caravan Show Birmingham NEC at the Elddis stand. They are probably the future for caravan security tracking, because they also recover the caravan if it gets pinched! have heard good things on other forums too.
Hope this helps