The Lockdown in 24 Season 1.
Lockdown is the name given to an inactive state of operations in CTU. Lockdown is declared usually when there is a security breach within CTU, or when a mole among the members of staff is suspected or discovered.
A lockdown restricts access to the CTU computer systems and networks for all staff, and the CTU security teams block entrances to stop anyone from entering or leaving the building during the lockdown.
Members of the CTU team can be searched and checks on the system are carried out during security breaches. A lockdown is indicated by flashing red sirens, klaxon sounds and a freeze effect applied to the computer systems.
Division shut down CTU and declared a lockdown on Day 1 3:00am-4:00am. The lockdown was requested by Tony Almeida and done by George Mason in order to hold Jack Bauer. Jack, however, escaped to his car, assaulting an agent in the process. A further lockdown was carried out in the final hours of Day 1 when Nina Myers's cover was blown at CTU and she was suspected to be a security threat. During this lockdown, Nina put in to play a contingency plan and made contact with alliances of hers in Munich, Germany and deleted and took copies of her confidential files, before killing Teri Bauer when she discovered what Nina was doing.
A lockdown was initiated when Ostroff managed to infiltrate CTU using Lynn McGill's keycard during Day 5 between 6:00pm and 7:00pm. However, the lockdown was converted to a Code 6 evacuation upon the discovery of a canister of Sentox Nerve Gas being introduced to the CTU ventilation system, and then was revised again when it was discovered that the gas was traveling from the perimeter inward, so that certain rooms were sealed to biohazard standards. Due to the circumstances surrounding the lockdown, evacuation, and eventual emergency sealing, roughly 40% of CTU staff perished.