I just wanted to share a side project that I have been hacking on. It's called Sonar (https://github.com/databat-io/sonar) and the idea is to use a Raspberry Pi to collect metrics of the amount of people in the surrounding area wirelessly (using Bluetooth and WiFi). You can then get sleek reports of the amount of people in the area (or rather, rough estimates). The typical use case would be something like a retail store, where you want to know the amount of people coming in every day (and see trends).
I did a brief write-up on Hackster today (https://www.hackster.io/vpetersson/sona ... ail-b17cc1) that outlines how to get up and running.
The project is still in its early phase, but it does already work.
Let me know what you think.