## Facts

- A Florida officer stopped Clayton Harris’s truck for an expired registration tag and observed nervous behavior and an open beer can.
- After Harris refused consent to search, the officer conducted an exterior sniff using Aldo, a trained narcotics-detection dog.
- Aldo alerted at the driver’s-side door handle, and the officer searched the truck without a warrant.
- The search found pseudoephedrine and other materials used to manufacture methamphetamine, not any drugs Aldo was trained to detect.
- Harris was later stopped again; Aldo alerted, but nothing was found.
- At a suppression hearing, the officer described Aldo’s training, certification, and ongoing training records; the defense focused on certification and alleged field “false alerts.”

## Issues

1. Whether a drug-detection dog’s alert, supported by evidence of training and certification, can establish probable cause to search a vehicle under the Fourth Amendment.
2. Whether the Fourth Amendment requires the State to prove a dog’s reliability through a rigid set of evidence, such as detailed field-performance records and false-alert data, before an alert may supply probable cause.

## Decision

- The Supreme Court unanimously reversed the Florida Supreme Court and reinstated the trial court’s denial of suppression.
- The Court held that probable cause is assessed under the totality of the circumstances, not a mandatory evidentiary checklist.
- Evidence that a dog has been reliably trained and certified in controlled settings may support a presumption that the dog’s alert provides probable cause, subject to challenge by the defendant.
- On this record, Aldo’s training and certification supported reliability, and Harris did not meaningfully undermine that showing; the search was supported by probable cause.

## Legal Principles

- Probable cause is a practical, common-sense determination based on the totality of the circumstances, rejecting rigid rules and mechanistic inquiries.
- A dog’s satisfactory performance in certification or training programs conducted in controlled settings can be sufficient to credit the dog’s alert for probable-cause purposes.
- Field-performance data is not constitutionally required and may be misleading; controlled training and testing records may be a better measure of reliability.
- Defendants must have a fair opportunity to contest a dog’s reliability through cross-examination and other evidence, including challenges to standards, testing results, and training practices.
- An alert is not automatic probable cause in every case; reliability evidence and adversarial testing remain relevant to the probable-cause inquiry.

## Conclusion

The Court held that a trained and certified drug-detection dog’s alert can establish probable cause to search a vehicle when, under the totality of the circumstances, the State shows the dog’s reliability through controlled training or certification evidence and the defendant fails to rebut that showing with meaningful contrary proof.


Florida v. Harris, 568 U.S. 237 (2013)