I have a friend who was "reminded" by his first employer that he had signed a non-compete after he changed jobs to a second (competing) employer. He ended up finding a third job at a company in a somewhat different field.

This was in Ohio where non-compets are enforceable, and the courts likely would have sided with the first employer if it had gotten to that point.

I don't think he ever realized what he had signed until he was "reminded" of it.