Bypass single entry fob system

kristamacg · January 31, 2024, 2:45am

Hey all!

I used the proxmark 3 to clone my apartment building fob which gives you access to the buildings and the parking garage. I gave a key fob to my girlfriend but the problem is – the parking garage has a system where you can only have one car entry per fob at a given time. So, my partner can’t park in the garage if I am already in there (even though I have a tandem parking spot, they still only allow 1 car since I am the only one on the lease – silly). I would have to fob out in order for her to fob in BUT, you cant just walk up to the reader and fob out, you have to actually have a car in the laneway in order to use your fob. They really got this thing locked down!

I’m pretty sure it expires after a certain amount of time and no longer stores the data showing I am still in the garage because last week I was able to let my friend into the garage when I had already been home for a few hours. Though, I am not entirely sure how long before that happens and it’s a pain regardless because that would mean I can only have a visitor if they arrive and depart some X amount of hours after I do. So for example, if we both want to arrive or leave around the same time – the first car would get in (or out), the second car would get an access denied.

Are there any fun hacks to bypass this? Something I can do with the proxmark so that my card still works but somehow the reader cant recognize the time frame as to which its been used?

amal · January 31, 2024, 2:55am

Check for a sensor you can easily block while you use your fob? Typically this is an IR sensor that the car breaks (an emitter on one side and a receiver on the other) or an ultrasonic sensor that points down from the ceiling.

That’s about all you can hope for unless you want to start playing around with randomizing IDs and seeing if anything triggers it… but then you’d be messing up someone else’s day haha

To be clear, the log data is not stored on the card or chip (or very very unlikely)… so you’d need to access the control board directly to mess with the history log)

StarGazer1258 · January 31, 2024, 5:07am

Could also be an inductive loop style sensor buried in the ground before the gate. If this is the case, you’d need something large and metallic to trigger the sensor. Something like a length of steel pipe, or a bicycle laid down over the sensor. The easiest way to check for one of these sensors is to look for a patch of concrete that is cut out in a circle or rectangle in front of the gate.