I am a contraption, with a door and a key,
But I don't keep anything else inside of me.
I can be found in offices and schools,
And I'm used by people of all ages.
What am I?
Answer:
A computer.
Explanation:
The contraption is a computer. The door is the keyboard, and the key is the power button. The computer doesn't keep anything else inside of it, but it can be used to store information on a hard drive. Computers are found in offices and schools, and they're used by people of all ages.