- Use a preliminary method of distance location to narrow down the number of phones that need to "test" against. In this case, Bluetooth.
- When a phone has established "neighbours" (other phones within 10-15ft), it tells them to prepare for a noise at a specific frequency via Bluetooth. It makes a noise at a specific frequency beyond human-hearing.
- It records the time that it emitted the frequency and sends it to the "neighbours", also via Bluetooth.
- Having been told to listen out, if they hear the specific frequency, the "neighbours" record the time they heard it.
- From this, distance can be determined. This is approximately 1m per 3ms delay.
Additional information can improve this estimate:
- The local temperature
- The position or orientation of the phones