How can I tell from a page within an iframe, if the parent itself is also within an iframe?

Explanation:

My home page home.html contains an iframe

<iframe src=sample.html></iframe>

I need to detect if home.html (ie: parent of sample.html) is within an iframe.

Code in sample.html:

if(self==window)

{

    alert('home.html is not in iframe');

}

else

{

    alert('home.html is in iframe');

}

My question is not a duplicate. It's a different case.