Spying on competitors: Identifying retargeting pixel?

I'm trying to spy on how my competing media buyers are doing their campaigns. Obviously I can see their ads and landing pages etc. But what I'm in the dark about is how they are doing their retargeting.

How do I identify the retargeting cookies that get placed on my computer when I visit their site? Is there a convenient way of finding out how they are retargeting and what other ad networks' retargeting cookies they are placing etc. ?

If you want to know if they are using Facebook Pixel for their retargeting look for code in their site:

<script>(function() {
var _fbq = window._fbq || (window._fbq = []);
if (!_fbq.loaded) {
var fbds = document.createElement('script');
fbds.async = true;
fbds.src = '//connect.facebook.net/en_US/fbds.js';
var s = document.getElementsByTagName('script')[0];
s.parentNode.insertBefore(fbds, s);
_fbq.loaded = true;
}
_fbq.push(['addPixelId', 'thierID']);
})();
window._fbq = window._fbq || [];
window._fbq.push(['track', 'PixelInitialized', {}]);
</script>

-Sasha