http://ithoughts.de/downloads/Setup_based_on_SSID.kmmacros
This keyboard maestro macro checks if you’ve just arrived at work or at home based on the SSID you connect to, and executes another macro you specify (in my case something that activates / deactivates applications and sets window sizes depending on the number of connected monitors, but it can be something easier, like turn on Skype at work and turn it off at home). Only a change of SSIDs from home to work or vice versa will trigger a change.