United States v. Knotts

1983-03-02

Headline: Court allows police to use a hidden radio transmitter to trace a chemical drum and locate a suspect’s cabin, permitting evidence found there to support a drug search.

Holding: The Court held that using a beeper to follow a container’s movements on public roads did not invade a reasonable expectation of privacy, so the tracking and resulting evidence were lawful.

Real World Impact:

Permits police to track vehicles with electronic beepers on public roads to locate suspects.
Allows tracking information to support search warrants and criminal prosecutions.
Leaves open whether secretly planting a tracking device on property is lawful.

Topics: electronic surveillance, police tracking, privacy and searches, drug investigations

Summary

Background

Federal agents suspected a drug conspiracy after a co-worker stole chemicals. With the seller's permission, officers hid a radio transmitter (a beeper) inside a five‑gallon drum of chloroform. They followed the drum by sight and by monitoring the beeper from Minneapolis to a codefendant and then across the state line. When visual surveillance failed, helicopter tracking picked up the beeper near a cabin owned by the defendant. Officers used that location and further observation to get a search warrant and found a meth lab; the defendant was convicted.

Reasoning

The Court asked whether beeper monitoring invaded any reasonable expectation of privacy. It said following a car on public roads gives a reduced expectation of privacy because travel and stops are exposed to public view. The Court found the beeper only assisted in observing what could be seen and was not used to monitor inside the home. Relying on earlier privacy cases, the Justices held there was no Fourth Amendment search here.

Real world impact

The ruling allows police to use electronic tracking devices to follow vehicles on public roads and to use that information to obtain warrants. The Court did not decide whether secretly planting a tracking device in property is lawful and left that question open. Because the Supreme Court reversed the appeals court, the evidence supporting the warrant can be used in the defendant's prosecution.

Dissents or concurrances

Several Justices joined only the judgment and warned the opinion used broader language than needed. Some urged caution about deciding planting beepers or applying open‑fields reasoning here.