When you exit the secure area of the airport, you usually pass through a corridor with tons of CCTV cameras and a TSA employee. Those cameras and that employee are to keep you from turning around and re-entering the terminal once you've begun the process of exiting.
You are responding to something totally different than what I was saying. Yes, we all know that there is a one-way exit from security zones in airports.
When you are passing through such an area, you are free to move unless you are detained, which in theory would not happen without good reason. The idea is that you are free to exit and just cannot go back in.
When you enter one of these chambers, you are detained by default until you are released. You are not free to go in any direction. It is very different.
I was responding fairly specifically to "I have never encountered a situation like this before in an airport."
edit: the operative word in your sentence is "_like_" and "_never_"
My point is, you have encountered systems "like" this, if you have ever exited an airport secure area. And it's the secure area, not the airport building itself.
I once encountered a big self-revolving door exiting the secure area at an airport, and I wondered what would happen if I kept going around it in a circle. Let me tell you what happens: it alarms loudly, and the TSA employee was not amused.
When you exit the secure area of the airport, you usually pass through a corridor with tons of CCTV cameras and a TSA employee. Those cameras and that employee are to keep you from turning around and re-entering the terminal once you've begun the process of exiting.