Illinois v. Caballes

If you're lawfully stopped for a traffic violation, police can use a drug-sniffing dog around the outside of your car without a warrant — as long as they don't extend the stop beyond what's needed for the original violation.

A dog sniff during a lawful traffic stop does not violate the Fourth Amendment if the stop is not extended beyond its original purpose.

Drug dogs can circle your car during a traffic stop without a warrant. But per Rodriguez (2015), they cannot extend your stop to bring a dog.