Ring the Bell

Passing an office building late one night, a blonde saw a sign that said, “Press bell for night watchman.”
She did so, and after several minutes she heard the watchman clomping down the stairs.
The uniformed man proceeded to unlock first one gate, then another, shut down the alarm system, and finally made his way through the revolving door.
“Well,” he snarled at the blonde, “what do you want?”
“I just want to know why you can’t ring the bell for yourself?”