geofencing inside a building

Hello Arduino Community,

Project Specifications:

A major part of the project is to create a geo-fence. It is planned that there will be a hub, used for hard computing and UI, centrally located in a building and a micro-controller attached to an individual. The micro-controller attached to the person must be able to alert, via wireless communication, that a person has left a room. We have our own ideas about how this should be done. However, I am not so certain that our approach is the most efficient or effective. The building will have WIFI, but it is preferred that it is self-contained.

[u]What sensor or communication device would be best for tracking movements in a building within 1.5 meter (5 ft.) accuracy?[/u]

[u]If we decided to implement this on a large scale would your suggestion still accurately track location with multiple devices implemented at the same time?[/u]

[u]What if it was a multi-floor building?[/u]

Project Equipment:

We have not bought components for the project yet and we are willing to spend approximately $25.00.

It should be assumed that we have a majority of the smaller components necessary to build simple circuits.

Controllers, Processors, and FPGAs we currently have collectively: 1. Raspberry Pi 3B 2. Arduino Uno 3. STM32F303 - Nucleo 32 4. Parallax Propeller Activity Board 5. Terasic Cyclone IV DE0-Nano

Level of Experience:

Three people are involved. Myself and one other in the group are studying to be Electronic Engineers and the other two in the group are studying to become Computer Engineers. We are all juniors who have worked on technical projects before and we have plenty of time to order any suggested sensors/devices and complete the project.

I want to thank you all in advance for your thoughtful comments and forgiveness if I have left out information necessary for a complete response. ;)

Look up "indoor localization". Especially for multiroom and multistory buildings, it is difficult and expensive to implement.

For single rooms, Pozyx seems to work well and is Arduino compatible.

https://create.arduino.cc/projecthub/Aritro/security-access-using-rfid-reader-f7c746?f=1

Is the requirement really 1.5 meters absolute position or is it that "a person has left the room"? The latter can probably be done reasonably well with IR transmitters on the person and a network of receivers across the rooms, the former is much more difficult.

If you find a solution, do not tell anyone, it would be a project that would be a huge commercial sucess, if it could be built for $25.