I think this homebrew key by Laurent Dumas (F8BBL) is simply amazing. It’s portable, easy to make from spare parts lying about the house and can serve you well if you’re in a pinch. (Sorry, I just can’t use this pun enough).
Admittedly, I think there would be some serious operator fatigue if you tried to use this key in a contest. But for emergencies–it certainly fits the bill!
If you can’t see the embedded video below, simply click this link.