Google Alarm browser add-on makes noises when Google collects your data
Whether it's Google.com, YouTube, or any site with Google Analytics, chances are you've picked up some Google cookies during your browsing travels. If you want to know when that's happening, Google Alarm is the Firefox or Chrome add-on for you.
I shouldn't make it sound like it's going to be beeping at you and popping up alerts nonstop (there's a no-sound option, too), but I don't necessarily want to install an extension that tells me when my data is being sent and then doesn't give me a way to prevent it. There are already popular alternatives, like Ghostery, that offer similar alerts and the option to stop your data from being sent when you don't want it to.
If you're worried about what Google's servers know about you, I recommend you skip past Google Alarm, and give Ghostery a try. It works on Firefox, Chrome, and IE. There's also another Firefox add-on called BetterPrivacy, which focuses on removing never-expiring cookies like the ones Google uses. Check both of these out and see which one might be right for you.