Perhaps you carry around a mobile hotspot, or a smartphone or smart navigation system? Many of these devices allow connections via other wireless technologies, such as Bluetooth. Often these devices have a default security PIN such as 0000, 1234 or 9876. None of these are particularly difficult for an attacker to guess! Make sure you change these PINs to something secure. Where possible, limit use of "discoverable" mode so your devices aren’t as easily found by attackers. Finally, disable wireless when you don’t need it.