This is something that I've been looking into as well. I can get 15% off my insurance with a vehicle recovery/tracking system. LoJack is damn expensive, between $600 and $1000 depending on the features that you're looking for. It's pretty packed with features, such as being able to start or unlock your car from a computer or cell phone, and the Early Warning system that tells you if your car even moves.
Way too expensive for me. And the idea of using the cell phone hidden in the car, well, thats a good idea, but I'm not so sure my insurance would accept that as a viable prevention tool.
One option that is cheaper (mind you, NOT cheap) is called a Zoomback. The only reason I know about these is because I install car electronics at Best Buy, and I had this lady come in saying that her husband had us install a Zoomback in her Tahoe, and now they're seperated and he's using it to stalk her. Needless to say we hunted for it and removed it.
Anyways, they're $100-$150. They do require an agreement (like a cell phone company) and also a monthly subscription of $10 per month. They require power, but not much, and are weather resistant. In the lady's Tahoe, we found in the rear bumper.
This is a much cheaper option. Any system that you find is extremely likely to require a monthly service fee. The LoJack systems don't, but thats half of why they're so expensive. Also, with the Zoomback, I'm not sure if an insurance company will accept it as a tracking system, since it is mainly meant to track family members, such as new drivers or recently estranged spouses.
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