If they cannot prove you drank that beer, which you first say you did, I would talk to a lawyer. Just to make sure the company didn't say anything about this incident on your Dac.
You said you arrived Friday, had a beer Saturday, waited around the check the student in Monday and THEN were going to be home. In that time line, it seems that you drank while still available to work. Sounds like you were doing home time on Monday after checking in the student. I wouldn't leave that information out there. If you don't say anything, it is up to them to provide evidence that you broke the company policy.
May be your policy saying before 24 hours and after 24 hours of your shift , as you mentioned Aside from this, if you yourself if pretty sure that you did not do anything wrong then try to fight back to prove you are right, and if you feel you were in a questionable setuation then forget these all and stop wasting your time.
Well if you told them the same story you told us, First learn to don't say anything, why would you answer a security guards questions, bad idea.
Cafeful with these D Bags out there. Dont go within a mile of work or your truck when you drink , them back row days are long gone.
Don’t drink alcohol and return to your truck. If you do obviously don’t drive. Stop talking so much, and if you’re going to lie keep it simple and short. Also “I used hand sanitizer” (most are just ethanol anyway) No one in a position of “authority” is your friend. Period. Don’t trust people. “In God I trust, everyone else keep your hands where I can see em”