Let's get this started...
You will need a Bluetooth-enabled phone and a Mac with Bluetooth and you'll need to connect your phone to your Mac using the Bluetooth preference pane (within System Preferences). You will not need to send any data between the two devices. Proximity works by checking on an interval see if it can "see" your phone. It will then execute AppleScripts based on that information. Bluetooth is the perfect protocol to use due to its short range being roughly 20-30 feet.
You can download Proximity here and the developer requests that you make a donation if you really like this application.