<font face="Verdana, Arial, Helvetica" size="2">I have to say that I thought it was all a bit much ado about nothing until my 170a flight test for my instrument rating. I was changing xpndr codes (on standby ).
I glanced down to check the code before I switched the thing on and blow me if I didn't find the thing reading 7700 and an examiner waiting expectantly...</font>
All this really argues for is care in changing codes. I never turn mine off (but then mine is 20 years old and likely the switch would fall off if I did). I'm just carefull not to turn the first digit through 7.
-me