Transponder does a what?

[LarryEWaiex121]

Just a note of something strange that happened to me this last Sunday. One of those gremlins no one seems to have an easy answer for.
I was doing a quick maintenance flight and told tower I was going to climb to 5,500' and remain about 2-5 miles north just orbiting. They were cool with that.
I fly in circles for about 20 minutes and decide for my arrival I'm going to fly further out and let down gradually to pattern alt. because of strong thermal activity in the area.
I get down lower and announce my intention at 10 miles out, I'm inbound for landing. They cleared me a straight in for 20 and call 3 miles final. All went to plan and the arrival was a non event. Switch over to ground and they clear me to my hanger. Just before shutdown I get a call from Grd. One two one Yankee Xray, you still up? Affirmative.
The controller said, "we just got a call from approach control and they said you had two instances of approximately 5-7 seconds each where you flashed "emergency". Clearly the code was 1200 and had not been touched the entire flight.
I said, "ok, guess I have something to check into".
Today I go out to my local radio shop where I occasionally do business and asked what that meant? Beyond the obvious. They all said they had no clue and had not heard of such a thing before.
I got the number of the tower from airport ops and gave them a call today. Talked with the guy who received the call from approach and he admitted he'd never heard such a thing before either. He was stumped.
I called Trig avionics by way of Mid Continent Instruments and Avionics and the guy I spoke with said he has been there many years and yes, he had heard of this happening 2 other times. The previous times were so long before that he had no memory of what the cause or fix was at that time. His suggestion was to send the unit in and have it tested thoroughly. Plus any firmware updates that may be needed.
Still not letting this go, I spoke with a gentleman from the local FSDO in Spokane and same story. He had never heard of such a thing. Only thing he was familiar with is a temporary code switching that accidentally cycles through critical codes like 7700 on their way to some other code. He said ATC is pretty much used to quick and fleeting flashes of wrong code and just ignore them.
Transponder is off for service. I'll wait to hear the results. If anyone has insight that could add context to this dilemma I'm all ears.
Larry
Waiex 121YX, Just shy of 1100 airframe hours and 13 yrs of fun.

[GordonTurner]

Does the transport have a switch to select emergency directly?

If so, some kind of intermittent internal switch failure may be sending 7700 when it makes contact.