Comment by tbensky

Back during the pandemic, hardware-based contract tracers were an idea. I built one using the ESP32; see https://github.com/tbensky/npct. In a nutshell, everyone generates a (non-centralized) hash for themselves based on local entropy. This hash is set to the BLE name of the ESP32. Turn it on and throw it in your backpack as you go out. When two ESP32s pass by each other, they both log the other's BLE name (hence hash). Later on, hash logs could be inspected and uploaded to a central server so you can see who encountered who. Seems like there's still some (non-Covid) applications for this (but I can't think of any). Fun project. Learned a lot about Bluetooth.