Squawk Codes:
1200: VFR flight, this is the standard squawk code used in North American airspace when no other has been assigned.
7000: VFR standard squawk code for most European airspace.
7004: Aerobatic and display code.
0021: VFR squawk code for German airspace (5000 feet and below)
0022: VFR squawk code for German airspace (above 5000 feet)
0001: Military code for highspeed uncontrolled (non-ATC directed) flight (US)
7001: Sudden military climbout from low-level operations (UK)
2000: The code to be squawked when entering an SSR area from a non-SSR area (used as a VFR squawk code in some European countries)
0000: military escort (in the US), suspected transponder failure (in the UK).
Emergency ones:
7700: Basic in-flight emergency code. This code will cause alarms to go off at all stations that pick it up and grant immediate attention from air traffic controllers monitoring the area.
7600: No radio (or lost verbal communications). This code lets controllers know that a radio failure has occurred on the plane. Planes with a radio failure are given priority over other, non-emergency traffic, and ATC will communicate with them via aviation light signals.
7500: Unlawful interference (hijacking) code. A plane squawking this code will be given any assistance requested.
Normally you can mantain it on 1200 although it's for VFR purposes.
