Press the bell

Passing an office building late one night, the blonde saw a sign that said, "Press bell for night watchman."
She did so, and after several minutes she heard the
watchman clomping (踏着重步)down the stairs.  The uniformed men 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 wanted to know why you can't ring it yourself."