Some kind of breathalyser attached to your computer that stops you going on the internet when drunk. I thought it might be a good idea for mobile phones too but that would strand loads of people without a taxi after an evening enjoying life's pleasures. I'm been trying to work out a way to block myself from Particracy unless I'm sober for ages, my current idea is some sort of cryptic password based on crossword clues that I won't be able to work out when I'm drunk, but I've no way of knowing whether I'll remember the answer or not. (Which is what I did the other night when I decided to leave, I changed my password to gobbledegook that I wouldn't be able to remember. Unfortunately I forgot that Particracy emails you a new password if you forget it )
Any ideas for useful inventions we haven't yet got?