Refer to figure.
The SSR transponder (Secondary Surveillance Radar transponder) is an onboard equipment that automatically responds to the ATC interrogations (ground equipment signals) and provides information to the air traffic controller screen such as identification of the aircraft and its position (bearing and range). Each aircraft uses or 'squawks' a specific 4-digit code which relates to its flight and is provided to the pilot during the ATC clearance. However, the following apply:

• When the pilot is experiencing unlawful interference or high jacking, the SSR code should change to 7500.
• When the pilot is experiencing radio communications failure, the SSR code should change to 7600.
• When the pilot is experiencing a distress, the SSR code should change to 7700.

This is a quick way to inform ATC about an emergency situation. The code '3612' is NOT one of the codes to squawk in case of an emergency condition and it relates to a code given by ATC for a specific flight.

Note: The term 'sqauwk' means setting a code on the transponder.