Great idea! Three things:
- we need it to also send out sound at 18kHz-22kHz wavelengths to block ultrasonic tracking via mics (so it needs a speaker).
- Altoids tins are effective Faraday cages, so a bad idea for this purpose

- CCO is getting the proximity of people to billboards directly from a cell data partner (was AT&T, not sure who now). That data is then correlated via Cuebiq and Ubimo (for the shiny RADARView map)