An engagement and wedding ring were among the items taken during a raid at an house in Blenheim Court, Belper.
After smashing a rear door window with a trowel that had been left in the garden the culprit used a key left in the lock to gain access.
Five rings and a bracelet were then stolen during the theft on June 20, which took place some time between 8.30am and 3.45pm.
A Deryshire Police spokesman said: “Never leave the key in the door lock as this can tempt an opportunist thief.”
Anyone with any information should call 101.