Chemical manufacturer 3M Company informed a Minnesota Bureau of Criminal Apprehension narcotics officer that Tristan Armstrong (defendant) was stealing chemicals used to make drugs. Police began investigating Armstrong and learned that he purchased additional chemicals from Hawkins (Hawkins) Chemical Company and delivered them to Darryl Petschen (defendant). Hawkins allowed police to place a transmitter called a beeper inside a container of chloroform, which they gave to Armstrong during his next purchase. Using the beeper and visual surveillance, police followed the container to Knotts’ (defendant) cabin in Wisconsin. Over the next three days, the police gathered enough evidence to obtain a search warrant. Inside the cabin, they found a fully stocked drug laboratory. The defendants were charged with conspiracy to manufacture controlled substances in violation of 21 U.S.C. § 846 (1976) and brought before the United States District Court for the District of Minnesota. Armstrong pled guilty and testified against Knotts and Petschen at trial. Knotts filed a motion to suppress on the grounds that the use of the beeper without a warrant violated the Fourth Amendment. The motion was denied, and Knotts was convicted and sentenced to five years in prison.