"For the most part, they're opportunists," said Lt. Kevin Hall of the Pasadena Police Department.
Victims don't discover the theft until long after the burglars have left, police said.
"They want to find easy targets. They're looking for windows that are open," Hall said.
Police reminded the public of the importance of keeping windows and doors locked.
Anyone with information on the suspects should call Pasadena police at (626) 523-0315.