Detecting KeyDown Script Does Not Work?

I am making a hta file, I have made a script in it to detect keydown but it never seems to work. Below is my code.

HTML Code:
function detect(){
if (event.keyCode == 27){
window.location = "1.htm";
}
else if (event.keyCode == 116){
return false;
}else if (event.keyCode == 117){
window.location = "2.htm";
}else if (event.keyCode == 119){
window.location = "3.htm";
}else if (event.keyCode == 120){
window.location = "4.htm";
}}
document.onkeydown = detect;