A minor point: you can't really measure distances by the speed of light via Bluetooth, the protocol is too coarse-grained. Bluetooth distance measurements are usually done via signal strength. However, time-of-flight distance measurements can be done on an extension of wifi called 802.11v - this is how the Apple Watch proximity unlock works, for example.
> this is how the Apple Watch proximity unlock works, for example.
I wonder — do you know if the proximity unlock only detect the relative distance between the computer and AP and compare that to the distance between the watch and AP? Or is it between the watch and computer?
The former would make sense to me, because my proximity unlock doesn’t always work immediately and it would make sense if it was because my watch and computer were connected to two different APs in my house (because one of the other hasn’t switched to the closest AP yet).
It is the direct time of flight between the computer and watch. However, the way Apple implemented it, the devices both connect to an AP first to mediate the connection; it's similar to how Airdrop connects two computers.
