Write an Arduino program for the lock-unlock system.

Write an Arduino program that should work on the Bluetooth module HC-05, which is connected with a nano Arduino board and compatible with smartphone Bluetooth. It should work like a lock-unlock system means if I am close to a Bluetooth device it can unlock the system and if not close to it then lock it as per the range of Bluetooth with a compatible device.(( I don't want to operate my system by a switch system in it. ))