In the movie Ex Machina, Caleb reprograms the security system to unlock all doors when there is a power cut. When the 10PM power cut happens Ava gets out. In the end when Caleb is locked in, he tries to access the computer. At this time there is a power cut. Shouldn't this have triggered all the doors to be unlocked for him to escape? Instead we find Caleb smashing a locked door with a stool, which means the doors didn't unlock when the last power cut happens. They don't show Ava changing any security protocols or anything. How come the doors don't unlock?
It's a little clearer in the screenplay that the computers shut down, not because the power had gone out, but because Caleb attempted to use his own access card in the card reader. Since the power was never out, the doors remained locked.
He runs back to the monitors. On them, AVA has reached the MAIN ROOM. She walks straight to the smashed window. And steps through.
CALEB sticks his card into the slot by NATHAN’S computer. Instantly, all the screens die. Replaced by a single word.
It is because Caleb programmed the room of Nathan to remain the only room locked after 10pm so that Nathan stays locked while they escape...