This attachment script from John Conrader notifies the user of an opened and closed garage door event. The script, as written, requires growl 0.6 or later and a Stanley Garage Door Indicator. It could also be modified for other setups.
After downloading, drag the _garage door attachment.scpt_ file into:
_/Library/Application Support/Perceptive Automation/Indigo 2/Scripts/Attachments/_
Read the script comments and create the needed devices and variables in Indigo. Restart Indigo or reload the attachments. Open and close your garage door and see the notifications.
When the garage door goes up, it will send a notification through growl at a priority of 2. When the garage door is closed it sends it at a priority of -2. Of course, these priorities can all be changed in the script.