How to deal with BackKeypressed()?

My game need to back mai menu when user push the wp8 phone’s BACK key, How to write my BackKeypressed() in unity3d or VS2012?

Like on Android devices, the back button is bound to the Escape key. So you can query the Escape key in an update and act accordingly

void Update()
    if(   Input.GetKeyDown(KeyCode.Escape) ) HandleBackbutton();

source - link text
user - spacefrog

void Update () {
if (Input.GetKey (KeyCode.Escape)) {

               or something else