At one home, the thieves took diamond earrings worth $2,500. At another, in the 1100 block of Oak Knoll, they took $110,000 worth of antique watches.
Real estate agents have compared notes and found a pair of women who attended every open house where a robbery occurred. They described themselves as mother and daughter.
Agents say one walked with a limp, and the two sometimes spoke in a foreign language.
Pasadena police says their investigation has been hampered because not everyone has reported the thefts.
Anyone with information is urged to call Pasadena police at (626) 744-4522.