Great idea per se

When developing for kinect or Nintendo DS, no problem maybe, but everything else might be.
Because you have to assume, the player has a mic and its connected right and everything

not a huge requirement, but could fail.
I mean there are even people in like ventrillo who dont have a mic =D

I think it's a fun idea, although maybe biased with people just don't make any noises, like I would

of course you'd have to filter, sounds from the game from the input of the mic
because if the dont use a headset, it obviously feedbacks into the mic, especially when something louder happens in the game

good thing is, the mic doesn have to be of good quality, for a simple check of volume

nintendo tried an interesting idea with the vitality sensor, where they measure your heart beat, allowing them to accordingly adjust stuff like music and intensity of the game. Hasn't been released yet though, probably because it didn't work well enough.

That's good idea. I'm on engineering so I know how to measure heart rate with "simple way". You can search it on internet and build your own. The problem is for PC, I dont know how the way in Java to access serial data (heart rate) from USB.

the game wouldn't have to depend on the extra device. But it could be some kind of bonus.

The device to monitor your heart rate could be awesome as well for a game. You'd have to control your fear irl
Like with the mic, like cero was saying, some people can be scared but still remain quiet. Some others can probably not control it enough to not talk :p

If you blink even once, the devil will appear and scratch you then disappear before you open your eyes

if there's another person in camera beside the player, the game wont start. you have to play it alone.

if it detect light of lamp or candle, it wont start cause you need to play it on dark room

if you scream like there is no tomorrow after find evil, game will give you a little HP so scream a lot

if you pee on chair, game give you extra score

if you win, the game will upload the video of you in scare to internet