No elevators don't work that way, when you have someone using a elevator and you press the button it will not stop is movement and come down again, what it does is, it finishes is last work, that is bring up the person and them it will go down to do the second request. IMO it is more realistic this way and more fare to the player, is not cool if you are half the way up and them a guard presses a button and you have no way to escape but face the guard, again IMO is better that the guard waits for the elevator to come down and them go up to chase the player or if the are some stairs he can use them to try to catch the player as he goes out of the elevator. And if you want to make it even more realistic you can make some kind of system that if the guard is far from the player as it enters in a elevator but near some stairs you could teleport it to the upper floor, make it in a way that the player don't see the teleportation and do not make it a instant one, make some estimations like this " if player is at X distance from the upper floor and the stairs that the guard would have to use have X meters taking in account the guard run speed them teleportation would take Y time" this will give a nice randomness's to it some times the guard will catch the player and some times it will not, in this way you guys save some "running up stairs" AI coding, but if he is near the player as he enters a elevator them make it wait for the elevator to come down. This only works in elevators that are not open like platforms and the player can see all the guards movements. p.s - I'm no coder so i don't know if this is more easy to do them to make the guard really run up stairs but it does sound cool.
