Wraith relay device
Device believed to be concealed on many worlds throughout the Pegasus Galaxy. The technology is receptive to Wraith transmission devices. When a signal is detected, a transmission is relayed to a Wraith ship capable of taking action against the intrusion.
The relay technology is particularly sensitive to Ancient life signs.
Suspicion - Dr. McKay deduces the presence of hidden Wraith relay devices on many worlds as the only explanation as to why the Wraith can track the team and take action so quickly.