About those space beeps...

You know, those beep tones sent right as the folks at mission control unkey a mic when talking to a spacecraft.   They're called "Quindar tones" and are explained here, at the SWLing Post.  Huh, and I always thought they were simple confirmation beeps.

More can be found at Wikipedia, along with the more modern CTCSS system.  CTCSS is used on virtually everything radio now, from space comms down to common GMRS walkie-talkies.