WASHINGTON – Can you trust what a dog’s nose knows? Police do, but the Supreme Court considered Wednesday curbing the use of drug-sniffing dogs in investigations following complaints of illegal searches and insufficient proof of the dog’s reliability.

Justices seemed concerned about allowing police to bring their narcotic-detecting dogs to sniff around the outside of homes without a warrant and seemed willing to allow defense attorneys to question at trial how well drug dogs have been trained and how well they have been doing their job in the field.

“Dogs make mistakes. Dogs err,” lawyer Glen P. Gifford told the justices. “Dogs get excited and will alert to things like tennis balls in trunks or animals, that sort of thing.”