Access Control System Fun

Back in 2015, the company I was working for at the time was renovating an office that was bought from another organization. This organization used HID iClass readers for their access control system. When my employer started moving into the building, our security company replaced the iClass readers with standard HID prox readers. They left one of the iClass readers in the trash so I took it to learn from it. Learn I did! Just to deviate a little bit, I’ve always found access control systems really awesome. Back in 2006, my school district opened a new high school. Since I was working for the IT department, we were some of the first people in the building. Heck, we were allowed in when it was still technically under construction (yes, we had hard hats issued so we could go in!). One of the first things I noticed was that there were these square boxes everywhere. I’m sure you’ve probably seen them.

HID ProProx II Reader

I learned that these were part of an access control system. As an employee, I got issued a keyfob so that I could get around the building. See, with it being a school, even back then, they implemented this system to prevent movement in lockdown situations or after hours. Like if you were to break one of the giant windows in the library, you wouldn’t find yourself able to progress anywhere in the building – just out a standard exit. Anyways, being fascinated with these, I always wanted one to play with. But, it turns out, they are very expensive.

Fast forward to 2016. I had just moved and unboxed my desk and came across my iClass reader. I started searching YouTube and found some interesting videos. This lead me to Amazon (naturally) where I found an access control system board. I picked up the 4 door board so I could play around with multiple readers.

“Hacking” in a missing feature

So while it wasn’t so hard to get this wired up and working, I noticed a feature missing that I think is pretty important. When the door is locked, the reader light should be red. This is the default state. It’s a pretty universal indicator – red = stop. When a valid credential is present, the light does turn green. However, the light goes back to red before the door is re-locked. If the lock is unlocked, either remotely or by time schedule, the reader still stays red. Why is this a problem? Some businesses have these on their front doors so employees can come in but visitors can only enter during business hours when the door is unlocked. Or maybe there’s a shared space that is unrestricted at times, but then after hours it’s restricted but the door is normally closed because it’s a fire door. Human nature is to know that red = stop (stop signs are red, traffic lights indicate red to stop). How would someone know if the door was open or not?

On some high end systems, I’ve seen this implemented. It might be a feature of the controller software, but in this budget board it’s not. So you have to “hack” it in. Checking my multimeter, I noticed that the reader block LED terminal has 5 volts across it normally. When a valid credential is passed, 12 volts goes across the line and then after a second, the voltage drops to 5 volts. So the green LED only illuminates when it senses high voltage (“high” meaning anything over 5 volts). Low voltage or no voltage means the line is off.

Green means go

With the mag lock, I have a jumper wire going from the NC terminal to the orange wire on the reader. When a valid credential is present, the NC terminal gets 12 volts across it and the mag log disengages using the common terminal. This means that when the lock is unlocked, a green light is shown on the reader for the entire duration! Success!


Here is a photo of the setup on my bench. You can see that the mag lock is secure as the reader is red and the light on the mag lock is green.

And even though this is a photo, it demonstrates that when unlocked, the reader stays green. There is no light on the mag lock indicating that it has no power.

I was able to add in the “missing” feature by doing a little bit of “hot wiring” the green LED control to the NC terminal on the block. Since the voltage gets passed across this terminal for the entire duration of the lock being unlocked, the light thus remains green during the entire unlock period. Even if the the lock is overridden via the control software, the reader will be green.

One issue

The only issue here is based on how you look at it. In this application, the reader also turns green if a REX (request to exit) is triggered – either infrared sensor or button. This may be considered undesired as it will always turn the reader green.

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