A working master branch in a continuous integration environment is key for fast development. While we hack line after line into the project, we merge back to master branch often even while the feature branch is still in development.
Merging early and often helps to avoid merge conflict hell because otherwise feature branches move too far apart. But this comes at the risk of breaking the master branch build. If that happens, the developer in charge has to stop his ongoing task and fix stuff immediately.
Until recently we used emails to notify the team of a failing build. But since email is old-fashioned, we hacked a signal light to show us the current build status. Follow the instructions below if you want to build your own Jenkins Traffic Light: