The Supreme Court held in United States v. Jones that prolonged GPS tracking infringes upon a Fourth Amendment interest, but left for another day whether that means that a warrant is required for all such surveillance activity. Building on Supreme Court precedent that directly addresses the problem of "standardless and unconstrained discretion," we propose that courts test the constitutionality of police action of this kind by examining the adequacy of procedural safeguards and actual police compliance therewith. Accordingly, in a range of settings involving new technologies, the state would need to craft reasonable safeguards against standardless discretion, and then comply with those safeguards in order for state action to be deemed constitutional.