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Updated 12-2-17:

After about half a year of having the Fastrak transponder hidden within the dashboard, the transponder stopped responding to the toll booth. I was worried about getting tickets due to the scanner not being able to read my transponder. It turns out that a photo is taken every time you pass the toll booth. That photo is used to link your license plate to the account on file. If the license plate is found on file, it deducts the toll charge from the account, otherwise a ticket is issued.

To be safe, I took the Fastrak transponder out and put in in the storage tray right below the climate controls. This is a much more accessible location and much easier to the previous location I had it in.

Receiving the Fastrak Transponder

When I first got my Fastrak Transponder, my first thought was “wow, this thing sure is bulky”. As you can see below, it’s a fairly big white plastic box that is supposed to be mounted to your windshield.

how to hide fastrak transponder - transponder

I received instructions indicating the recommended mounting locations for the transponder:

fastrak mounting instructions
Image from: http://bayareafastrak.org/

I ended up mounting the Fastrak transponder to the alternate toll tag mounting location at the bottom left of the windshield.

how to hide fastrak transponder - original fastrak location
how to hide fastrak transponder - original fastrak location
how to hide fastrak transponder - original fastrak location from front of car

After a while of driving with the Fastrak transponder at this location, I just didn’t like that there was something on the windshield that seemed to affect my visibility. Normally, I don’t like anything on the windshield that blocks my vision (I always fold both drivers and passenger visors up if I don’t need them). I also don’t like the fact that I have to keep taking off and putting on the transponder every time I drive through the bridge toll. The transponder probably could be left on the windshield, but it may be susceptible to theft. I know, it’s probably not likely that someone will want to break into my car to steal a Fastrak transponder, but hey, the more empty your car looks, the less likely it will get broken into.

Where to Hide the Fastrak Transponder

And so, I started thinking of ways I could hide my transponder. I wondered what locations would be good for hiding it, so that I would never need to mess with it. Meanwhile, it still needs to have the ability to register every time I pass the bridge toll. I have an account set up with the transponder so that it automatically funds the account when it is low. So basically there is no need to handle the physical transponder.

First, I needed to understand when and how the Fastrak transponder is read. This image shows how the transponder is read through RFID (Radio Frequency IDentification).

how to hide fastrak transponder - bridge toll diagram
Image from: http://bayareafastrak.org/

Experimenting with Mounting Locations

I began experimenting with the placement of the transponder at different locations around the car to see whether the antenna was able to read the transponder. After driving through the toll booth many times with the transponder at different locations (at least twice in each location to validate), I ended up with the following results:

Location of Fastrak TransponderDid Bridge Toll Register?
mounted at lower left of windshieldYes
mounted at upper left of windshieldYes
mounted at upper right of windshieldYes
mounted at lower right of windshieldYes
mounted at lower middle of windshieldYes
mounted by rear view mirrorYes
sitting in sunglasses holder (above rear view mirror)No
sitting in cupholder by gear shifterNo
mounted at speedometer gauge locationSometimes

Final Mounting Location

What I learned from this experiment was that the transponder will have trouble being read at the toll plaza if there is metal between it and the antenna (e.g. sheet metal roof) or if is too far away from the windshield. When it sat in the cupholder, it did not read probably due to the distance from the windshield and in-turn the distance from the antenna at the toll plaza. Also, it had trouble reading when the electromagnetic signal was blocked from metal roof when it was placed in the sunglasses holder (above the rear view mirror). Although placed close to the windshield, the signal was still blocked by the roof. And finally, having the transponder sitting nearby the gauges in the car would intermittently get readings (definitely not reliably each time.)

I concluded that the most important things to keep in mind when hiding the Fastrak transponder is proximity to windshield and eliminating any metal component(s) between the antenna and the transponder. So, I relocate the transponder to behind the dashboard so that it would be somewhat close to the windshield, yet only have a layer of vinyl/plastic between it and the antenna. In order to gain access to the space behind the dash, I needed to remove the radio.

how to hide fastrak transponder - proposed location

After removing the deck, I mounted the Fastrak transponder in a space behind it. I wrapped it with electrical tape so that it wouldn’t rattle around.

how to hide fastrak transponder - hidden location behind radio

After putting everything back together, I drove through the bridge toll plaza multiple times. Each time I drove through, I could hear a faint beep through the dash. I’d see the display at the toll plaza reading “Valid Fastrak”, which indicates it was able to read my transponder. Now, I have a hidden Fastrak transponder that easily reads every time I go through the toll plaza. Success!

Now if I ever do plan on moving onto the next car, I need to remember to remove the transponder from behind the dash before selling it…


Hi there! I'm Scott and I run The Track Ahead. My goal is to provide helpful articles and tutorials based on my experience and research related to car maintenance and automotive detailing. When I'm not writing and not working my day job, you can find me spending time with my family and working on home and car projects.

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