Comment by IshKebab

Except... that pairing in Bluetooth 4.2 is still broken. And they apparently even used an algorithm from Bluetooth 2 that was known to be broken.

https://pomcor.com/2015/06/03/has-bluetooth-become-secure/

Basically Passkey Entry is broken so eavesdroppers can trivially learn the PIN. You must use a dynamic PIN (not always possible).

Oh and if you're thinking you can implement your own pairing method that is actually secure, via the Out-of-Band method, think again! Neither Android nor iOS support it.