<!DOCTYPE html>
<html>
<body>
<p>Press the "O" key on the keyboard in the input field to alert some text.</p>
<input type="text" size="40" onkeypress="myFunction(event)">
<p id="demo"></p>
<script>
function myFunction(event) {
var x = event.charCode || event.keyCode;
if (x == 111 || x == 79) { // o is 111, O is 79
alert("You pressed the 'O' key!");
}
}
</script>
</body>
</html>