That may be true, but regardless of the type of thief, i would rather my rig not move in the first place than to have to track it down by gps only to find it totaled from a joy ride, already disassembled at a chop shop, or somewhere across the border.
Jamming gps is not as expensive or sophisticated as you might think, and it is far simpler than circumventing encrypted key fobs and such. A simple jammer can be had for as little as $60, (example:
http://www.jammerall.com/products/Mini-GPS-jammer-for-Car.html ) and any 15 year old proficient with computers or electronics can build a jammer themselves. Anyone attempting grand theft auto would be idiotic to not invest in a jammer given the prominence of lojack, onstar, etc. these days.
As for shutting down on the highway, that seems improbable if the switch was wired between the battery and starter. The switch would control a high amperage relay that would disconnect the high current circuit powering the starter motor. This would not interfere with low voltage circuits (PDM or canbus), and if it did fail, it would only cause the vehicle to not start - not stall on the highway like a true kill switch.
This mod is much less complicated than something like an engine swap that folks routinely do on this forum (and in my opinion, probably less likely to leave you stranded), so it should be comparatively easy to do a starter switch properly. Plus, a starter switch does not require a data plan subscription. Of course, having both a starter switch and gps would be ideal.
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