Switching apps based on where user looks

I am using MBP with external monitor, in addition to the build-in display. It happens quite often that I 'mentally' switch to other monitor, but the active application is still on different one, where I don't look. Then I start typing, or press some shortcut which leads to unwanted behaviour (e.g. I close an editor tab instead of tab in the chrome).

I was wondering is there is any app, which would use camera to guess where the user is looking and switch the active app accordingly. I am sure that it would not be perfect, but I would give it a try.

Any other suggestions to deal with my problem are also welcome.

My answer falls in the "other suggestions" opening provided.

There's a tool called Isolator that may help you stop mistaking which app is in the foreground (and keep your focus in the right place). Here's the description from the tool's home page:

Isolator is a small menu bar application that helps you concentrate. When you're working on a document, and don't want to be distracted, turn on Isolator. It will cover up your desktop and all the icons on it, as well as the windows of all your other applications, so you can concentrate on the task in hand.

There's an option to make background windows blurry or semi-transparent, in lieu of simply hiding them. Witness the blur:

(source)

Reviews elsewhere:

• OS X Daily: Focus on Apps Easier & Apply Background Filters with Isolator for Mac OS X
• Lifehacker: Download of the Day: Isolator (Mac) – mentions two similar tools.
• MacApper: Anti-Distraction Apps: Keep Yourself On Task – (ditto)