I'm thinking about creating a physical lock, where the keys would simply be paired Bluetooth devices, but I'm concerned about the potential (in)security. I would like to have a Bluetooth 2.1 module constantly scan for paired devices and when one is found and successfully connected to (by the module), open the lock. Neither the 'lock' module or 'key' device will broadcast their Bluetooth address (since the module should already know the key's address from pairing), hopefully keeping the existence of them unknown to any 'bystanders'.
So my question is: using a long pairing PIN (e.g 20 digits) and assuming the pairing process isn't intercepted, would it still be possible to 'spoof' a paired device and therefore allow the module to connect to it?