Detect keypress in window

Is there any way to detect a key being pressed in the window? I have tried the following but it doesnt work:
document.onkeyup = KeyCheck;
function KeyCheck()
{
var keyID = event.keyCode;
alert(keyID )
}

I know this is silly but could you need a semi colon after alert(...);
If you look in the bottom right of the browser you might see an error.

// You may need a doctype (or use document.body) for ie.
// For non-ie you need the argument that is passed in non ie event handlers

Code:

---

document.onkeyup= function(e){
    e= window.event || e;
    alert(e.keyCode);
}

---

Thanks mrhoo that does exactly what i need :)