I) old mp3 with inbuilt speaker or ever cheap mp3 player will do.
II)Insulated copper wires.
V)touch switch found in CD roms.
VI)speaker motor metal strips
Step 1: Connection
the wires from the switch should be connected to the battery and motor.
the axle or the rod of the motor should be soldered with a strip of metal with a wire.
other side of the motor there should be a another strip of metal.
once the switch of the door is turn on the motor spins turning on the mp3 power wire the motor acts as a relay switch.
put songs on your memory card and insert it in the player .
now fit the switch downwards not touching the ground just few mm up .
now fix a piece of matchstick or whatever you want on the floor
so that when the door is opened the switch gets pressed.
Step 3: Check How It Works