Spartan

Robert Scott is a former Force Recon Master Gunnery Sergeant, acting as a selection cadre member for Delta Force. While observing an exercise designed to evaluate Delta candidates, Scott meets a recruit, Curtis, as well as Sergeant Jacqueline Black, a knife-fighting instructor.
Scott is drawn into a clandestine operation to find Laura Newton, the President's daughter, who is missing. Their search takes them to a bar where girls are recruited as prostitutes, and Scott's team follows a middleman to a bordello that funnels some of these girls to an international sex slavery ring. The madam gives them a contact number leading to a pay phone.
Calls placed to the pay phone are traced back to Tariq Asani, a Lebanese national currently in federal prison. They plan to intercept Asani during a prisoner transport and gain information from him about the sex trafficking operation.
When the car carrying Asani and another prisoner stops en route to its destination, Scott shows up and appears to kill the transport guard, then kills the other prisoner (who was on death row). He spares Asani when Asani says he can get them on a plane out of the country that night and confirms the sex slavery ring is based in Dubai.
Scott stops at a convenience store to relay the information to the team. Curtis provides him with more ammunition, but Asani, waiting in the car, happens to spot the badge of another agent talking with Curtis and opens fire. Curtis is wounded and Scott has to kill Asani.
As the team prepares an assault in Dubai, a news broadcast reports that Laura and her college professor were discovered drowned while sailing off the coast of Martha's Vineyard. The rescue operation is called off. Scott returns home, but Curtis tracks him down and persuades him that Laura is alive and shows Scott an earring that was caught in his mat from the beach house identical to those Laura is wearing in a news photograph.
When they return to the beach house, Curtis is killed by a sniper. Scott evades the sniper and finds Laura's unique sign in a window in the beach house indicating she was there, he realizes that she is not dead. He takes his pager and phone apart and finds a tracking device.
He tries to contact Laura's mother but he is intercepted by a female Secret Service agent assigned to guard the First Family. When he shows the agent the earring, the agent explains that for years the President has used visits to his daughter as a cover for extramarital affairs, and that he pulled Laura's Secret Service detail to use as extra protection for himself during the latest trip.
Scott enlists Sergeant Black to help him rescue the girl from Dubai and turns to Avi, a former Israeli operative. Avi agrees to get him into Dubai and smuggle Laura out concealed in a cargo container, obtaining weapons for him and support from a man known as Jones.
Jones is killed during the rescue and Scott flees with Laura to a safe house, where he persuades her that although he is alone, he is acting under orders. Correctly guessing that he is really acting on his own, Laura says that King Leonidas of Sparta would respond to requests for help from neighboring kingdoms by sending one man, and decides to trust him.
When he takes Laura to the airport to seal her in the cargo container, Scott discovers he is being tracked when he finds a transmitter hidden in his knife. He rushes her out of the container just as his old team arrives to apprehend them. Scott is shot and Laura is captured. Her captor reveals herself as Sgt. Black, who shows her the earring and photos from the Secret Service agent, convincing Laura to stop struggling. A Swedish news crew witnesses the struggle as they are about to board their own plane nearby, and recognize Laura. Black is shot by Stoddard, and a hysterical Laura is hustled to safety aboard the journalists' plane. Just as the jet takes off, Stoddard's throat is slit by Scott. An injured Black then asks Scott if Laura is now safe, which Scott confirms.
Later, on a London city street, a stubbled Scott is shown watching an evening news broadcast regarding Laura's return on a television in a shop window. The government spins the story of Laura's kidnapping as an opportunity for the President to take action to end the trafficking of American girls as sex slaves. A British man watching the news broadcast with Scott then says, "Time to go home," and walks away. Scott watches him leave and says, "Lucky man." Scott is then seen walking off into Piccadilly Circus.

Question: Where was the transmitter that was tracking Scott hidden?
Answer: knife