First, you might want to listen to the iBeacons episode.
Then maybe the episode with Simon and Pushcut in particular, though you may not get much on iBeacons specifically after listening to the previous episode.
In this thread post, Tony references how he does the automated triggering with a USB iBeacon plugged into a socket in the car. Such beacons are typically available through a variety of online retailers, I have a couple of different ones myself.