Firestone

The Firestone was a necklace worn by Lady Clemency Eddison, a gift from her Vespiform lover Christopher. Though she believed it a mere keepsake, the Firestone was actually a powerful telepathic recorder and transmitter. The Firestone was stolen by Robina Redmond, although she returned it when she was accused of the crime. Donna Noble threw it into the lake and when the Vespiform dived in after it, it drowned. (TV: The Unicorn and the Wasp)

The Firestone was recovered from the lake many years later and bought by Torchwood at an auction. (WC: Captain Jack's Monster Files)