Beacon is a little command-line tool that lets you connect a Delcom USB RGB LED light to a set of TeamCity builds and use that to get an irrefutable indication on whether those builds succeeded, failed or are under investigation.
To get started just run the following command-line:
beacon --url=http://yourteamcity.com --username=username --password=password --builds=build_id_1 build_id_2 etc
or, alternatively using TeamCity guest access and running only once with verbose logging:
beacon --url=http://yourteamcity.com --guestaccess --runonce --verbose --builds=build_id_1 build_id_2 etc