Frankly, it depends on any police that might come into contact with you at such a party. The police do not have to give you a breath test just because you demand one. If they believe that you were drinking they can file charges. Further, If an officer testifies that he believes that you were drinking a magistrate could find you guilty of the charge.
If you don't show any signs of having ingested alcohol, most officers would probably not cite you. However, as noted above there are no guarantees - by being present you potentially put yourself in danger.
The short answer: You can be charged if someone said you were drinking and you exhibit behavior that tends to support that. The long answer: Even though you were not drinking, I have seen cases where everyone gets cited for underage drinking, despite the absence of a breathalyzer test. In fact, there is a court case in Pennsylvania that states portable breath test results are not enough to convict for underage drinking or public intoxication and that a police officer must testify as to the nature and extent of the person's behavior in order to sustain a conviction. So consider this: You are nervous about getting cited or arrested and you stumble over your words as you speak to the police officer and then trip over the rug. Police officer will then testify you were "unsteady on your feet" and you "mumbled and stuttered" while he was speaking to you. That may be enough to sustain a conviction in front of some judges. The moral of the story is to stay away from such parties, especially once you turn 21 (which is a different issue altogether).
The answers I provide are not considered legal advice. Short questions in this forum do not allow for full and competent legal advice. I advise you get an attorney in any case where you have contact with the legal system.
Answered by Michael Kotik lawyer in Pennsylvania and New Jersey.
If your not drinking you should be okay. However, if the police officer is having a bad day, he might give you a citation just for being there. It has happened! If that happens just get a lawyer, assuming you did not drink anything and they have no proof besides your general demeanor, you should be okay.
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