The problem with monitoring systems is that they only monitor the ones that comply, that is those who do not need monitoring. The ones who do need monitoring usually circumvent the systems anyway.
I had a friend when i was younger, he worked for a company, that fitted and maintained tracking for Taxi companies.
Essentially their system always found the closest available car, and dispatched it, but in the city centre, there were a lot of taxi's so within certain distance barriers it would also try to balance the taxi drivers fares, it essentially had a list, and if you were in the city centre, you got a trip, based on when your car was there.
The taxi drivers hated it because if they got a trip outside of town, they would have to drive all the way back to the city and they only got onto the list in the city centre when they got back. So they would essentially have to drive 30 minutes to get back into the city centre, and then they started at the "back" of the electronic line.
So, some of the taxi drivers found that if you disconnected the GPS antenna, the system would not know where you were, and ask the driver, where he was, and he could enter "City centre"
Sometimes this would backfire if it was a busy night, at they would suddenly be at the top of the list, while still being out of town, so costumers were fuming, when he took 20-30 minutes to arrive.
The company that managed these taxi's asked my friends company, what they could do, so they ended up modifying the software, so that if the car had been without GPS signal for X minutes, Y amount of times, their system would go into a fault state, and the driver was out for the rest of the night and had to go to the shop and have the system diagnosed and the error reset.
Cost him money in lost fares, and the bill for the diagnosis, so it did not take very long before these units stopped losing their GPS signal
Just goes to show that those who are intent on cheating, will find a way.