Riddle

I turn around once. What is out will not get in. I turn around again. What is in will not get out. What am I?

Choose an answer

A.A lock
B.A door
C.A latch
D.A key
Hint: It's a 2-word phrase with 4 letters, starting with "A".

Answer

A key

Why this is the answer

Turning a key one way locks a door (keeping intruders out); turning it back the other way unlocks it (letting whoever's inside back out).

This riddle is filed under Logic Puzzles and Brain Teasers and rated Medium.