It's an application on try icon that unmute microphone on a keypress
When the Application strat, it will add a status icon. Hold Right options key to talk, and release to mute
The icon indicator will be translucent if microphone is muted.
Application Installer (dmg) can be downloaded in the Release Section
The app is from an unidentified developer
I did not sign the App. To enable exception for this app follow https://support.apple.com/kb/PH11436?locale=en_US
If you want to be sure, just compile the project, Archive & export PushToTalk.app