The emergency exits in the stations used to, and the signs still say "alarm will sound if opened", but they were disabled around 2014 because there were too many false alarms. Mostly because the emergency exit doors are also used for strollers, luggage, etc. that can't fit through the turnstile, or as a general exit when there's a large group of people exiting.
Case Neistat did a New York Times Op-ed video on YouTube about it, before they were disabled: https://youtu.be/aUcP5OD-ctQ
Wrong emergency exit. What they meant was the emergency exits from the tunnels themselves, which are located halfway between each pair of stations and lead directly to the street via unassuming yellow hatches in the sidewalk.
You'd be paying somebody to stand there all day at multiple points for each station. This isn't a situation that happens once a half hour, it's every minute or so.
What's an alarm going to do? Unless someone is right there to apprehend the suspect, and that's unlikely, the alarm is just going to go off and then what? Someone disables it 10 minutes later? That doesn't help identify the suspect.
The cameras are probably deployed to prevent crime, and there's very little crime in the tunnels because very few people are stupid enough to risk their lives by entering them. Besides, the tunnels are dimly lit.
There's 220 miles of subway tunnels (though not all are underground). On top of that one can simply just use a dollar store ski mask to avoid camera identification.
But they have to get into the tunnel first, probably from the station. If anyone is able to enter the tunnel from outside, then it is dangerous, because they can put a bomb or a crowbar on the rails.
>Then, he disappears, most likely through the subway tunnels and out an emergency exit.