This should answer that question quite nicely for you...You aren't gonna like the answer...lol.
Can Thieves Disable Gps Tracker? - LegalProX
If you put a portable signal blocker inside a stolen vehicle, you'll be able to stop the tracking signal. A thief might use a handheld RF detector to find alegalprox.com
Tracking Blocker, I'm not surprised the thieves figured that out
That GPS tracker puts out a signal every 2 hours So that gives a thief plenty of time to disconnect the tracking