Lojack is a one-time install fee of around $500, and then you have to pay for service if it's stolen or older than 5 years (I think that was the minimum battery life). Lojack's system is hooked into the Federal NCIC (National Crime Information Center) and when installed your lojack is associated with your vehicle's VIN. When you file a police report with that VIN, it goes into the NCIC and Lojack's network sees that - they send out an activate signal from a national network of towers, and that starts the vehicle's transponder broadcast. In a Police vehicle for an agency that supports Lojack (not all do), there is a radio direction finder array of four matched antennas on the roof of the vehicle:
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a small processor and a display for the officer:
When a LEO vehicle receives a "hit" (broadcast from a vehicle transponder), the display will light up in the cab with the transponder number and what direction the signal came from. With two or more receiving cars coordinating over the radio they can quickly triangulate down to the house/driveway/yard/shipping-container the signal is coming from.
That system is good if you live or travel in an area supported by Lojack.
If you want to do something yourself there are GSM GPS trackers available, but these come with cellular charges and service fees. Might as well get a prepaid Android phone and use the Google
where's my phone feature included for free. If you're a hardware hacker, I could see removing the vibrate motor and replacing it with a relay that disables the ignition circuit and activates the horn... Just need to hide the phone in the truck and wire in a car charger/solar charger. Keep in mind that if you're the only one who knows about this or how to use it and you get shot while being car-jacked - you're probably not going to see that again... There is a benefit to having it externally monitored/operated.