I'm pretty sure it would be illegal without an NSL. Tipping of the subject of an investigation over a search conducted pursuant to a valid warrant.

Would using a technology that makes a warning of surveillance unavoidable be illegal?

Would there be a way to expose the integrity of a service (actual devices connected etc), read only, to every user of a service? So that when an interception device or protocol is used, every user who cares to look (and can understand) would know about the disruption.

And then, when the government says "Stop doing that, we want to watch your users," the only way to do that and hide the watching would be to disable the system wide security view. And people make their conclusions.

They have an answer for that: the government installs black boxes that monitor stuff. That's why so many companies cooperate by giving them data, it's a lot better than having random stuff in your machine rooms with actions and purposes you neither control nor understand.

Has the supreme court ever ruled on NSL secrecy vs the fourth amendment?

I don't think there's really any overlap there. The overlap with the 4th would be less about secrecy and more if someone demanded full content from an account, since NSLs are not warrants (legality of procuring "metadata" without a warrant is the much larger issue there, but so far courts have been ok with it).

The secrecy part can be a violation of the 6th amendment (right to confront your accuser), but theoretically evidence procured under the NSL will be produced by trial time (except when shown to conflict with national security, which judges can sometimes accept too readily).

The real problem with secrecy is the first amendment, since you are forcing people to not divulge that they received an order to hand over information. Typically prior restraint like that is heavily circumscribed to protect an ongoing investigation but no further, which means that indefinite gag orders should have correspondingly extraordinary justification. Considering the hundreds of thousands of NSLs that have been issued, this seems unlikely to be the norm.

The first amendment approach has been successfully[1] argued by the EFF at the district court level. This has opened the way for more lawsuits, including an appeal of that case, which will hopefully make their way higher in the court system.

(read the linked EFF article if you're interested in more. It lays the case and the judge's ruling out in great detail)

[1] https://www.eff.org/deeplinks/2013/03/depth-judge-illstons-r...

I don't think it even got a ruling from a Federal Court yet, because the feds kept playing legal games, and got away with dismissing the cases. But I think it's been declared unconstitutional at least 3 times by normal Courts.

http://www.youtube.com/watch?v=DYsXCNLB0CI

It is usually ruled that the plaintiffs can't prove standing, meaning they can't prove they were harmed by the behavior. And of course one would probably need access to their raw data to prove standing, so its unlikely that the courts are the way to go. Even if the court does rule that its illegal it is almost impossible to enforce. The FISA court ruled that certain things were not permissible but the NSA did them anyhow.

Sorry, brain fart on my behalf, I had confused the first and the fourth admendment.