There are very few limits to the power of the All Writs Act -- the act, passed the same week as the fourth amendment, grants the <i>courts</i> (not the FBI) the authority to &quot;issue all writs necessary or appropriate <i>in aid of their respective jurisdictions</i> and <i>agreeable to the usages and principles of law</i>&quot;.<p>However, you actually have to get to the courts before the All Writs Act can be applied.<p>CALEA was passed to create a <i>preemptive</i> requirement for standardized wiretap interfaces&#x2F;equipment, processes, etc, prior to any actual judicial warrant or writ being written.<p>The fourth amendment grants us protection against &quot;unreasonable&quot; search and seizure, but doesn&#x27;t grant the government an affirmative right to require that <i>future</i> &quot;reasonable&quot; searches be easy, or possible.<p>It also (unfortunately, in my view) doesn&#x27;t prevent the government from requiring preemptive action to support future searches, and that&#x27;s what CALEA does.