My boss office has a beeper. When he wants to look for his secretary, he will beep the beeper. One night my colleague stayed late to do work. She is the only one in the office. Suddenly, she heard the beeper - beep! She got scared. She quickly packed her things and left the office. (Memory collected at the Cheng San Public Library during the "irememberGhost stories" campaign from 27 Sep to 30 Nov 2012)