A number of transponders have a ground & standby mode, which stops ATC approach radar pictures cluttering up with ground movements.
Here is an example:
http://www8.garmin.com/manuals/G1000:Non-AirframeSpecific_TransponderPilotsGuide.pdf5.2 OPERATION
MODE SELECTION
Mode selection can be automatic (Ground and Altitude modes) or manual (Standby, ON and Altitude modes). The STBY, ON and ALT softkeys can be accessed by pressing the XPDR softkey.
Ground Mode (Automatic)
Ground mode is automatically selected when the aircraft is on the ground. A green GND indication appears in the mode field of the Transponder Status bar. In Ground mode, the transponder does not allow Mode A and Mode C replies, but it does permit acquisition squitter and replies to discretely addressed Mode S interrogations. NOTE: Ground mode can be overridden by pressing any one of the Mode Selection
softkeys.
Standby Mode (Manual)
The Standby mode can be selected at any time by pressing the STBY softkey. In Standby mode, the transponder does not reply to interrogations, but new codes can be entered. If the Standby mode is selected, a white STBY indication appears in the mode field of the
Transponder Status bar. NOTE: In Standby mode, the IDENT function is inhibited.