RC Wonders in the UK is selling an alarm clock that is branded by Mensa.org.uk (although Mensa does not sell the clock themselves).
When the alarm goes off, you cannot turn it off immediately. First, you have to play a little game of Simon -- that is, the clock flashes a series of colored lights at you, and you have to repeat the pattern back to the clock. The patterns come in three levels of difficulty (your choice).
If you fail to repeat the pattern correctly or in the allotted amount of time, the alarm starts ringing louder. The alarm continues until you eventually succeed.
RC Wonders is also selling the clock through eBay.
I guess my question would be about AC power compatibility -- if it's made in the UK, can you plug it into the wall in the US? I guess they've faced this issue, since they specifically state how to buy from the US.