“Warrant canary” is a colloquial term for a regularly published statement that an internet service provider (ISP) has not received legal process that it would be prohibited from saying it had received, such as a national security letter. The term “warrant canary” is a reference to the canaries used to provide warnings in coalmines, which would become sick from carbon monoxide poisoning before the miners would—warning of the otherwise-invisible danger. Just like canaries in a coalmine, the canaries on web pages “die” when they are exposed to something toxic—like a secret FISA court order. Warrant canaries rely upon the legal theory of compelled speech. Compelled speech happens when a person is forced by the government to make expressive statements they do not want to make. Fortunately, the First Amendment protects against compelled speech in most circumstances. In fact, we’re not aware of any case where a court has upheld compelled false speech. Thus, a service provider could argue that, when its statement about the legal process received is no longer true, it cannot be compelled to reissue the now false statement, and can, instead, remain silent. So far, no court has addressed this issue. But if you’re not paying attention to a specific canary, you may never know when it changes. Plenty of providers don’t have warrant canaries. Those that do may not make them obvious. And when warrant canaries do change, it’s not always immediately obvious what that change means. That’s why EFF has joined with a coalition of organizations, including the Berkman Center for Internet and Society, New York University’s Technology Law & Policy Clinic, and the Calyx Institute to launch Canarywatch.org. The Calyx Institute runs and hosts Canarywatch.org.” See this FAQ for more information.