1. Run PixelMonitor.
2. Crosshair cursor appears; click or drag to select an area of your display for the program to monitor.
3. As soon as a single pixel in selected area changes*, a sound plays to alert you of the change. [and/or an alert window pops up, etc]
* (preferably this could ignore the mouse cursor floating by)

This would be great for letting you look/step away from your computer to, say, make your bed while you're waiting for some change in a program without a built-in alert system.

I have two slight modification ideas:
- change the three hotkeys to "tap Ctrl, then Ctrl+V [or C or X]" (with the current shortcut, the slight pause when normally pasting throws me off)
- (less important) a few toggle-able string processing commands (like collapse multiple newlines to just one, delete beginning and trailing newline(s), or maybe just user-customizable regexp capability)

Well, I recompiled it with AHK (deleted a couple line breaks - I don't know if that caused the problem), and it's working fine now.