It triangulates using cell towers as I would imagine it has a sim card.
You would need to find what frequency its at 800/800/1800 etc (this will depend on the provider) and use an oscillator (jammer) to also block that.
this will also drop the data connection it has that feeds the data back in real time (warnings, location).
Googling it, it's just an ODB device, so would use canbus.
If you wanted to fuck with it you could:
fit inline on the odb port a sniffer and canbus injector, have it never report over a certain MPH and stuff like that to get around the restrictions you want. this way they can still track you but no alerts will be triggered (speed, braking etc - although close speed can be determined from gps)
spoof GPS using a hackrf, this will get round the jammer detection and also stop them from tracking the vehicle location accurately)
easiest to get away with would be ODB spoofing, they can get your location but never accurate speed, braking or whatever you want to block
its a fair bit of work though as you need to sniff the individual packets to setup the filtering and spoofing. also not good if they have access to your truck
easiest to do would be the cell jammer but you run into a lot of troubles there, illegal, obvious, etc
It also seems they pay to scrub all info about disabling these off Jewgle too because there are NO posts, even on reddit, about how to disable Geotab beyond 2017. No car forums. Cant find shit. They probably pay some company to keep tabs so the Geotab employees dont leak the info we need to disable this gay thing. I wanna take the trash to the dump in my work truck, not my semi-decent personal SUV, you faggot HR Fleet fucks! Im so tempted to just rip it out and act like my boot got caught on it or something but i know its more trouble than its worth for the families sake
I have a solution for you, if you just want to take the truck on personal stuff without them knowing.
buy two ODB extension cables and cut them in half.
join the cable back together with one socket leading to two plugs (so spliced together)
unplug the geo and plug it into the socket and then one of the plugs back into your truck.
The geo will go off briefly and report this when it boots back up, just say you knocked it or something.
with the other socket end left, attach the two power pins of the odb connector to a 12v battery (do a lithium so you can charge it in the house while your are out, you only need enough juice in it to get from the truck to your home)
when you want to go on personal errands, plug the battery into the other plug on the Y lead you made, unplug geo from the truck and leave it at home.