Well, we had thousands of people violating the 4th Amendment willy-nilly looking at our email and phone data and it's taken years for that to credibly leak out. Bucking authority like that is not only unusual, it's downright rare. Don't count on it.

Not that I believe that there's a secret button.

However, keep in mind that the NSA doesn't employ that many people. Furthermore, these people mostly work in the same area, have been vetted repeatedly, and are watched. The TSA, on the other hand, works everywhere, has many more people, and do not have the same scrutiny applied to their employees.

Interestingly enough, most classified information doesn't get leaked the same way that Snowden leaked his documents. It's mostly due to carelessness. The best example of this is deployment schedules. One of my coworkers was scheduled to go on a Marine Expeditionary Unit (ship that goes around the Pacific just in case something happens). The date of departure was classified. Someone told his wife, who told all of her friends on Facebook. Oops.

If you include contractors whose primary income is from providing services to the NSA, the number of people who had some knowledge of their surveillance is probably approaching half of a million.

But even those contractors are professionals if they get access to anything of value.

Trying to keep a "detain"-button secret, having it manned by thousands of people that only have a high school diploma OR a year of work experience in security/aviation/screening, doesn't sound easy (those are by the way the education requirements for a TSO according to usajobs.gov). Since a leak could stem from a minor overstep of their contract (ohh, I told a buddy about it, big deal right?), and there are frequent policy violations by agents, it does look grim for the existence of such a button.

I heard of them kicking the machines to make them go off though, so there's a "button", and it's public knowledge that they will use it if they want a pat down.