Hmmm. Never thought of that, good suggestion.

I was taught a different method-- switch the transponder to standby first, then set the code. Same result, no chance of inadvertent 7700, 7600, 7500, etc.

And I would strongly recommend a tour of ATC facilities. I've visited Washington Center in Leesburg, VA (ZDC). Got about a 1-hour grand tour, including spending about 20 minutes sitting at a console with a sector controller with headphones patched into his communications. Very interesting indeed!
Security-wise, (this was pre-9/11, April 2000), the facility was rather non-descript, but surrounded by fences and signs that it was a restricted area and that tresspassing, disruption, etc. could lead to loss of life (referring, I assume, to airplane passengers, not to the tresspassers). No obvious sign of guards, etc.