Another mod idea from the n00b

My newest idea is based on science fiction. It may already exist, but I dont know about anything like this around. There is voice recognition for EVERYTHING. Install some software and you can talk to your computer and make it do ANYTHING. Not exactly. I have yet to see a computer program that can recognize ur voice "Computer: power on" since the program needs the computer to execute. My idea is to make a piece of harware that when plugged in, is always on. Its only job will to listen for "system start" or something. When it hears that, it will send a signal like you have pressed the power button. (it would also listen for "System restart" if your machine freezes). CAN THIS BE DONE? and what do you think of the mod?