I had a solar-powered pocket calculator with a membrane once. Credit-card-sized. You can tell I was a nerd because I owned three pocket calculators at the same time.
Yes, but the 400 had it on a spillproof membrane like you'd see on a fast-food cash register. The later models improved the layout but most had much worse switches than the 800.
The 400 if you acidentally stepped on it it'd flip back and bark your shin, you'd fall over and put your foot through it. that's why there's so few today.