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)