it seems to work as is, I was wrong, chrome on mac book is not going into the "real compass" section. should have tested it, maybe.
if (window.DeviceOrientationEvent && 'ontouchstart' in window) {
// setup real compass thing, with event.alpha
document.body.innerHTML = "haz!";
} else {
// setup some mouse following hack
document.body.innerHTML = "nope";
}
check yourself: http://jsfiddle.net/benzkji/J58ef/
remains what happens if a touch enabled windos laptop with deviceorientation enabled chrome is showing up. probably check the "absolute" property of the deviceorientation event: https://developer.mozilla.org/de/docs/WebAPI/Detecting_device_orientation