"The tool I ultimately chose for the purpose of the detection itself is a little free app appropriately called Proximity. This is a thin little program that does one thing, but does it well -- that is to sit in the background and scan for a given Bluetooth device at regular intervals. When it detects a change in the device’s availability, it simply calls one of two Applescripts: One for the device leaving range, and another for when the device enters range.
So, armed with that I set out to create two Applescripts that would perform the following tasks:
When the Bluetooth Device enters range:
•Deactivate the Screen Saver Password.
•Deactivate the Screen Saver.
•Reconnect the phone to the OS X Address Book
•Sync the phone using iSync
When the Bluetooth Device leaves range:
•Activate the Screen Saver Password.
•Activate the Screen Saver."