i've heard of that from a county jail. no one can open the doors from that locations, they all have to be remotely operated and the guards usually use their portable radio to as dispatch to open it for them
yes, those explanations are 100% accurate. Sallyports are great because the cop drives in with the badguy. The port doors are closed, so that if the cop opens the door, and badguy goes beserk, he really can't run anywhere. Totally trapped! Also think about how tough it would be for a cop to get an unruly suspect into the station if it was wet or icy out. major problem. Access control is a very big part of any modern police station. This is just one part of the whole access system.