How familiar are you with electronics and SW development?
You need to do some both on Arduino and on your Android phone.
- close the door too
- send a secure code that differs per time => so if the code is intercepted during the day it can't be used in the night.
- learning mode
- multiple androids for one garage door (kids/wife/dog whatever)
- multiple garage doors with one application (code send depends on geo location)
- depending on time of day the arduino switches also lights on/off
- add timeslots when this app may work (e.g. it will only work between 06:00-23:00 over bluetooth)
I would start with
0) go throught the tutorial section of arduino.cc to learn about the platform
1) an Arduino opening the door
2) closing the door
3) learn about bluetooth & serial communication
4) develop the android app (might take several steps in itself)
5) merge both of them
6) think over the security algorithm
7) do 6 again
implement the security algorithm
9) test it
Can i use an arduino BT with a transistor on an output pin to complete the circuit...?
Yes but better use some relays because that separates the circuits.