<p>A warrant canary is a posted document stating that an organization has not received any secret subpoenas during a specific period of time. If this document fails to be updated during the specified time then the user is to assume that the service has received such a subpoena and should stop using the service.</p>
<li><ahref="https://en.wikipedia.org/wiki/Warrant_canary#Companies_and_organizations_with_warrant_canaries">Companies and organizations with warrant canaries</a></li>
<li><ahref="https://www.schneier.com/blog/archives/2015/03/australia_outla.html">Warrant canary criticism by Bruce Schneier and an example of a law against warrant canaries.</a></li>