Canines patrol grounds daily

(CNN) -- Canine noses, hundreds of times sharper than those of humans, make dogs integral members of law enforcement agencies.

Trained to detect bombs, bodies, accelerants or drugs, dogs find what humans will miss.

Tony Ball, spokesman for the Secret Service, said the dog that alerted security officers to a suspicious car on the White House grounds Thursday morning was trained to detect bombs only.

Secret Service dogs make routine runs on White House grounds throughout the day, every day, Ball said.

Other federal agencies such as the U.S. Customs Service, the Drug Enforcement Administration and the Federal Bureau of Investigation use dogs to find contraband, cocaine or criminals.

Most dogs are trained for a specific type of work. Accelerant-detecting dogs will not also serve as drug dogs. Cadaver dogs, however, will also participate in searches for lost people or fugitives because they are trained to detect fear-induced hormones the body releases.

What the dog at the White House did Thursday is called passive indication -- sitting.

"Most accelerant dogs or bomb-detecting dogs are trained to do passive indication," said Keith Herron, who trains cadaver-hunting dogs for Child Connection, a nonprofit agency based in Kentucky. "Most crime-scene dogs -- bomb, accelerant -- are trained to be passive. You don't want a bomb dog to be aggressive. Everybody would go bye."

Dogs perform the work for rewards, food or special toys. On days when the dogs are not involved in investigations, their handlers hide the scents or objects they are trained to seek to keep them sharp and to maintain the work-reward practice.