um . . I have a keychain that is a little blue disc, about 1.5" in diameter. It says "Fermilab" on it, and has their cool logo. It is transparent, and on one side there is a switch which causes a red LED to light up.
I never leave home without it, because it is attached to my keys which I need to leave home.
And it is, um, very useful. It cures cancer, and has a full copy of Half Life 2 on it. That it can play with a neural interface in my head.
They are only a few dollers, so drive up to chicago and buy one.