[dbloom]

It's worth surfacing the fact that California's FasTrak transponders beep when they are being read (although it certainly might be possible for the beep to be suppressed).

By the way, in addition to LAX, this also happens when you're looping around San Jose Mineta airport (SJC). The airport says that it's to track taxis, limos, and shuttles: http://www.mercurynews.com/search/ci_14885277

[mrb]

FasTrak CAN be read without the transponder beeping (the beep is software-controlled by the reader): the Transportation Corridor Agency themselves explain they are being read at many highway exits to calculate traffic stats. And I have never heard my transponder beep when exiting the highway.

[dandandan]

They suppress the beeps on the 15 in San Diego. It used to beep at the single tolling location when there was only one (and read many other times for traffic flow / variable toll calculation) but they eliminated it now that there are 10+ points where it is read to determine distance traveled. The only place it beeps in SD is on the 125.

[mbreese]

The beeping at SJC drives me nuts, since at SFO you can use the FasTrak to pay for parking.