Im using HC-05 Bluetooth, an android phone and ATMega644 arduino.
When I pair my android phone to the bluetooth is there a possible way so that the bluetooth will reject the pairing if the android phone used is not my phone and only pair with my phone only? 
anyone?
Can you set a pairing PIN that you don't tell anyone else about?
Can you make the bluetooth module 'non-discoverable' so other devices can't find it and ask to pair?
To answer the question we would need the manual for your particular bluetooth module and if you can point us to the manual you should first read it yourself to see if it contains the answer you seek.
Hi, sorry for re-float this topic. Could you get any way to read mac address for your purposes? I'm trying something similar.
If I can't, I will create a variable in the phone with a unique ID (set manually) and send it to arduino, and in its sketch, check this ID for validate it.