Wraith homing necklace

"So some Athosian thought this would make a nice little necklace?"

- John Sheppard

Teyla's necklace is a Wraith tracking device which is dcesigned to track Ancients.

Overview
The necklace was used by the Wraith to track down Ancients during the war. The device was activated when an Ancient touched it, most likely sensing the ATA gene. The device is not very powerful being unable to transmit through subspace instead relying on other Wraith technology from picking it up.

History
Teyla Emmagan had this necklace when she was young but lost it in the Athosian caves. It was found in 2004 by Major John Sheppard who activated it without knowing and gave it back to Teyla. Teyla continued wearing this, having their team attacked by the Wraith numerous times offworld, until it was discovered the true nature of the necklace. Knowing this the Atlantis expedition used the necklace to capture a Wraith.