How do I deploy PIR sensors to track people's entrance and exits of a room? [duplicate]

Question

I want to deploy sensors to the door to a private room in order to track people's presence in the room. These are the requirements:

1. sensors must be outside of the door;
2. it should detect both entrance and exit or whatever it takes to know there are someone in the room;
3. due to the nature of the room, it can be assured that at most one person will be in the room at one time;
4. the sensor should be able to communicate with a computer using either wifi or other wireless medium.

It has been pointed out by this post (What sensor to choose to track human presence indoors?) that PIR sensors can be the solution. However, I know very little of electrical engineering. I'd really appreciate it if you could explain this in details, e.g. what components to buy, where I can buy them, how do I collect the sensor data from a laptop using wireless media, etc.

I have a background in computer science, so the actual coding should be less of a problem.

Answer 1

To keep track of whether a room has an occupant you only need a PIR sensor in the room. This is easier, and possibly more reliable than monitoring direction of movement through doors (and allowing for pranksters exiting windows etc)

I'm assuming you don't implant RFID tags in all potential visitors.