Adipose Industries pendant

The Adipose Industries pendant functioned as a portable inducer. When twisted, it activated the birthing process of Adipose within the wearer. They were given away free with every three-week Adipose pill course.

The Tenth Doctor attached two necklaces to a larger inducer to cancel out Matron Cofelia's master inducer. The Doctor used his and one stolen by Donna Noble. Penny Carter also stole a pendant. (TV: Partners in Crime)

Information from invalid sources
The gold pendants included bioflip-digital-stitch circuitry that allowed Matron Cofelia to track the Adipose after parthenogenesis. (PROSE: Doctor Who: The Encyclopedia)