While 7700 may be the special squawk code we most often hear about, there are others. They serve the same purpose - to provide easy notification to anyone monitoring the aircraft of the situation. These are all (including 7700) defined by theInternational Civil Aviation Organization (ICAO). Ph...
In an emergency, a pilot should squawk 7700 which means set his or her transponder to that set of digits so that it returns that code to Air Traffic Control. This indicates that the aircraft is in distress. The other meaning of 'squawk' is a report of something broken on the aircraft...