Ring

A ring was an item of jewellery which was placed on a finger.

Rings could be used as bio-dampers. The Tenth Doctor gave Donna a bio-damper in the form of a ring so that she would be hidden from the Racnoss. (TV: The Runaway Bride) Gavin wore a bio-damper ring he inherited from his father which hid his alien origins. (TV: The Empty Planet)

John Hart was in possession of a ring that could emit a tracking signal to last 5,000 years. He threw this ring in with Jack when he was burying him. Its current whereabouts are unknown, but likely either still in the grave, in Jack's possession or in Torchwood Three's possession after they dug Jack up. (TV: Exit Wounds)