Generate a question about the following movie plot: Jessica Martin (Kim Basinger), a high school biology teacher, takes her son Ricky to the school bus. After she returns home, several men kidnap her and confine her in the attic of their safe house. Ethan Greer (Jason Statham), the group leader, smashes the attic's telephone. Jessica uses the wires of the broken phone and randomly dials a number. She reaches the cell phone of Ryan (Chris Evans), a carefree young man who has just been dumped by his girlfriend, Chloe (Jessica Biel). Jessica persuades Ryan to go to the police station, where he briefly reports to Mooney, but has to leave to avoid losing connection. Ethan asks Jessica about something, which she denies knowing, and leaves to get Ricky. Overhearing them, Ryan gets to Ricky's school, only to see the boy kidnapped. He hijacks a security officer's car and gives chase. When his phone battery runs out, he takes the gun in the car, cuts in line at a shop and buys a charger. Deciding to check on Ryan's kidnapping claim, Mooney goes to Jessica's house. At the house, he finds Dana Bayback (Valerie Cruz), the kidnappers' accomplice, posing as Jessica. Believing the claim is a false alarm, Mooney leaves. With Ricky in tow, Ethan returns and asks Jessica about a place her husband Craig mentioned, "The Left Field", and learns that it is a bar at the Los Angeles International Airport. A cross-connection between phone lines causes Ryan to rob a nearby lawyer's cell phone and car. At the airport, Ryan plants the gun on one of the kidnappers, which trips the alarm. When security intervenes, the kidnappers flash police badges and apprehend Craig. After viewing a news report of a man holding up a store for a charger, Mooney identifies Ryan and calls Jessica's home. He notices the voice on the answering machine is different from that of the woman he met. The kidnappers learns that Craig put a videotape in a bank safe deposit box. One guards Jessica and Ricky, while the rest go to the bank. Ryan finds the box first and leaves with the video camera, but loses the lawyer's...
What does Ryan plants on one of the kidnappers which trips the alarm?