Tom is trapped on the top floor of a department store. It’s just before Christmas and he wants to get home with his presents. What can he do? He has tried

calling, even yelling, but there is no one around. Across the street he can see

some computer person still working away late into the night. How could he

attract her attention? Tom looks around to see what he could use. Then he has a

brilliant idea—he can use the Christmas tree lights to send her a message! He

finds all the lights and plugs them in so he can turn them on and off. He uses a

simple binary code, which he knows the woman across the street is sure to

understand. Can you work it out?