in the ancestral comment here, it wasn't even an alert system! It was just "your job is to sit there all day and watch every single transaction and flag the aberrant one"!!
"Whoa this transaction is way bigger than normal. So is this one. And this one."
People ignore repetitive things, but they usually notice when it changes. They can tell you that it's shaped different or explain how it sounds different from normal.
If this system made dissimilar transactions look very similar to the monitor, then it is to blame, not the idea of having a monitor at all.
