> Turns out the Mobile OS are making this kind of communication nearly impossible. To work well, it basically needs background job (automatic scan of nearby ble/wifi/radio) and automatic connection without user interaction (imagine being prompted to accept a connection every time you pass by someone), both have been basically made impossible (especially after covid).

Isn't this how some covid-specific apps work to let you know if you've come in contact with an identified carrier? https://www.gao.gov/blog/covid-19-exposure-notification-apps...