How are Bluetooth devices detected?

[mhixson]

From the ESP32 can it see Bluetooth devices that are nearby without those devices being in pairing mode? And if so are there still Bluetooth devices that can go undetected? Or is Paxcounter able to see every Bluetooth device that comes close enough?
Thank you.

[cyberman54]

Paxcounter detects BLE advertising packets sent on 3 signalling channels. Those are present, regardless if a connectable BLE device is in pairing mode, or not. Thus, also unconnectable BLE devices are seen. But only counted, if they have a randomized mac address.