PaulS:
How is your garage going to know that you are 100 meters away?
I was thinking of using geo fencing / geo location using a mobile phone to say "I'm near" via GSM, the receiving technology (Arduinio/ESP8266/Photon?) then operates a relay and opens the door.
PaulS:
How is the Arduino supposed to know that some phone (and that it is the proper phone) is 2 meters or less away?
Using technology! 
The end goal is ~2m away, working back from that aim, RFID could work with a large antenna but was thinking more along the lines of BLE or WiFi. All technologies could work, but rather than trying to re-invent the wheel wondered if others had tried anything similar / have recommendations!?
Commercially, new hotel's are using this type of tech on their door's to let guests in their rooms, I'm looking to re-create that experience at home!
Maybe a BLE module could work for both!?