Huntington, has used these doors, at E. Washington, by the Wal Mart, for a few years... Pendleton Pike branch, also .....Your statement is correct. In most cases, the metal detector is just part of what are called "man trap" doors. The basic premise is that you enter through the outer door and pass through a metal detector. If you pass the screening process, and the outer door is closed/latched, you will be able to enter through the inner door (a green indicator light will serve as your "all clear"). If you do not pass the screening, a teller or manager will be able to communicate with you via a two-way communication system (just like the drive-through). If your keys, or other acceptable item, set off the sensor, they will buzz you in. If they cannot identify what set off the detector, you can exit the way you entered. The doors also limit entry and exit to one person at a time (one coming and one going). It is also possible to trap/lock someone in between the doors.
The above description is an example from the bank I used to work for a couple of years ago. I managed a branch at 56th and Georgetown. This location was robbed at least once per year for six straight years (three times one year). The bank determined it was cheaper to install the doors, rather than hire a security guard. Since the doors were installed, the branch has not been robbed. The doors have been in place for three years. That said, the doors are a pain in the butt. They are very sensitive and required constant adjustment. For obvious reasons, they left a lot of customers upset. Having worked at a bank, I understand both sides of this discussion.