Multiple realities
(covers information from several alternate timelines)
The emergency lockdown was a feature on areas of a starship that was intended to lock personnel out of a dangerous area.
In 2258 of the alternate reality, Leonard McCoy ordered that the USS Enterprise's sickbay engage emergency lockdown while the ship was falling through Earth's atmosphere. (Star Trek Into Darkness)
In 2374, Alexander Rozhenko accidentally tripped an emergency lockdown on the IKS Rotarran locking himself inside a corridor, much to his embarrassment and the crew's amusement. (DS9: "Sons and Daughters")