Ever test the ant-stat bag by leaving the FasTrack in it when you place it on the dash at as you roll thru a toll gate.? If it works your Fastrak account shouldn't be debited normally but they will correlate your car to you via a plate reader. and you will get debited and you should see how they did it proving the bag actually works or not.
The reason I say this is because in some areas (NYC) the transponders are used for more than ease of toll payment.
https://www.youtube.com/watch?time_continue=25&v=JCwWVxGtYgE
The British series “Black Mirror” shows episodes like that and is quite good and sold on Amazon but curiously is in the PAL format and set for Region 2 in effect blocking it in the US.