What sensor to use to track human presence outside of a room from inside
Microwave.

It can penetrate a lot of materials, but not all. Depends on what the room is made of. Search for microwave detector.

There will be a detection field, some are adjustable.

You will likely then need to integrate to a microcontroller/microprocessor for WiFi and website.

Doubt there is anything off the shelf that will do what you want.

That's enough to get you started.