Programs: UA 1K MM, HH Diamond, IHG Gold, Marriott Gold, National Exec Elite, Avis Presidents Club
Update: I did notice that my transponder beeped just before I entered the terminal A garage and again down past where the terminal C baggage claim used to be. Both times it was when I drove under one of those transponders that I'm guessing tracks the buses.
No. Your transponders went off because a FasTrak-like system is being used to keep track of taxis, limos and shuttles to record trips and related fees. But officials say other drivers are not being charged. Someday FasTrak may be used for paying parking fees in the garage, but that is way down the road.