"Reply.. '' G-CD squawking, 1,, 2,, 3,, 4,, Request zone transit at 2000ft. '' ( Press each key as you call out each number.)"
Many of us have transponders which require each number to be set by rotating a knob, then pressing to set. If you take too long to get all 4:set, it reverts to previous setting.
I have no autopilot, and turbulence can put trimmed aircraft off settings.