What's the beeping noise on Bombardier cab cars?

I rode in a cab car on a Hudson Line train and noticed frequent beeping: usually 2 or 3 series of electronic beeps; sometimes more, but the last series would end quickly. The beeping occurred all along the route, including in Grand Central.

Curious what this is? I was in a Connecticut cab car with doors at each end- Charter Oak, I think.

Thanks.

Alerters now installed on cab cars.

Thanks, your reply is most helpful.

I won't be riding in cab cars from now on. That beeping is very annoying.

Then avoid the head cars of the electric equipment too...you can hear it through the closed cab door.

This is the best part about riding the head end.

on the SLE in both directions once you learn the sounds it tells you alot of whats going on