What happens if an Employer finds out you are using fraudulent information?

Lets say during an interview. Will they just tell you they can't hire you, or will they detain you and call the police, or tell you to leave and then call the police and hand them the fake documents?

It would depend on the person interviewing you I guess. But keep in mind that generally it's the background check that lets an employer know that you're not able to work due to whatever reason. The person interviewing you would probably just hand you the background check and tell you something's not right.

My advise, don't put yourself in a situation that could quite possibly get you in trouble.

It depends. They'll give you a call and tell you that your SSN(if you provided one) did not match your name and probably ask you to double check the number figuring they don't suspect you being an undocumented immigrant. Now you decide if you tell them your're undocumented and hence can't work for them or tell them that you will double check with the social security office and never call them again. Either way, you probably won't get hired, unless they're cool with you being undocumented and all.

I'll say, it depends the kind of job you're applying to.

Off-topic, but is that project diva?

On topic: It really depends on your interviewer, but you should use caution when presenting false documents.