## Facts

- DEA agents learned that several defendants ordered 50 gallons of ether, a chemical used in cocaine extraction, from a government informant.
- With the informant’s consent, agents placed an electronic tracking device (“beeper”) in one can of ether and delivered that can as part of the shipment to the buyers, who were unaware of the device.
- Agents tracked the ether’s movement from a defendant’s residence to other residences and to commercial storage lockers, using both physical surveillance and beeper signals.
- The beeper was used to confirm the can’s presence inside private residences, including a house rented by several defendants.
- Agents obtained and executed a search warrant for the final residence, relying in part on information associated with beeper monitoring, and seized cocaine and related evidence.
- Defendants moved to suppress the seized evidence as the product of unconstitutional installation and monitoring of the beeper.

## Issues

1. Whether placing a beeper in a container with the original owner’s consent, and transferring the container to an unsuspecting buyer, constitutes a Fourth Amendment search or seizure.
2. Whether monitoring a beeper constitutes a Fourth Amendment search when it reveals an item’s location inside private residences that could not be determined through lawful visual surveillance from outside.
3. Whether evidence seized under a later search warrant must be suppressed when some information in the warrant application was derived from unconstitutional beeper monitoring, or whether untainted facts independently established probable cause.

## Decision

- The Court held that installing the beeper with the informant-owner’s consent, and transferring the can to defendants, was neither a search nor a seizure.
- The Court held that beeper monitoring that merely tracks movements in public, or reveals no more than could be obtained through visual surveillance, is not a search.
- The Court held that monitoring the beeper to determine the can’s presence inside private residences was a Fourth Amendment search and required a warrant.
- The Court concluded that suppression of all evidence was not required because the search warrant was supported by sufficient untainted information establishing probable cause, and it reversed the lower court’s suppression ruling in substantial part.

## Legal Principles

- Consensual placement of a tracking device in property before it is transferred to a suspect does not, by itself, invade the suspect’s reasonable expectation of privacy or meaningfully interfere with possessory interests, and therefore is not a search or seizure.
- Electronic tracking that discloses only information obtainable by ordinary visual surveillance of public movements does not constitute a Fourth Amendment search.
- Electronic monitoring that reveals information about the interior of a home—such as confirming that an object is inside a particular residence—invades a protected expectation of privacy and is a search requiring a warrant.
- When a warrant affidavit contains both tainted and untainted information, suppression is not required if the untainted evidence independently establishes probable cause for the warrant.

## Conclusion

The Court distinguished permissible use of a beeper for public tracking from unconstitutional monitoring that discloses an object’s presence inside a home, and it allowed the search-warrant evidence to stand because probable cause was supported by independent, untainted facts.


United States v. Karo, 468 U.S. 705 (1984)