- "Activate the tracker. Let them know we're here."
The Tracker is a device used by S.H.I.E.L.D. It is intended to transmit the location of the item or person to which it is attached.
Upon discovering that Ian Quinn had recently purchased an unknown object developed by Cybertek, Coulson's Team planned to board the train transporting it in an undercover mission, in order to follow the package and trap Quinn.
The purpose of the mission was to attach a Tracker to the package, and then safely follow it to Quinn's location.
Leo Fitz and Skye managed to follow the package to the compound where Ian Quinn was receiving it. Before Skye entered the compound, Fitz activated the Tracker to let the rest of the team know their current location.
Thinking she was talking to Melinda May in sunglasses, Raina told Agent 33 that the point of a Tracker was so that she did not have to be tailed. Agent 33 told Daniel Whitehall that Raina had a tracking device. Grant Ward was able to find the Bus with Raina onboard, though it was cloaked, by tracing the signal that the Tracker emitted.
During a conversation between Daisy Johnson and Lincoln Campbell, where she attempted to ask him to be the transitioner for the newly-transformed Inhuman Joey Gutierrez, Campbell refused Johnson's request and attempted to walk away from her, disrespectfully. Alphonso Mackenzie, Johnson's partner, grabbed Campbell's arm, telling him that he would let Johnson finish her thought. Unknown to Campbell, Mackenzie placed a Tracker on him when Mackenzie grabbed his arm.