How can I leave the planet?

Hint 1 of 7:

Did you push all of the buttons in the aliens' room?

Hint 2 of 7:

Talk to the guard.  He will not allow you to leave.

Hint 3 of 7:

He wants your PDA, but it is too valuable to give away.

Hint 4 of 7:

Give him something that resembles a PDA.

Hint 5 of 7:

You have something else that is round, although it is the wrong color.