Was it illegal for my son to get a ticket for unopened alcohol?

What state and what jurisdiction?

It was not illegal, per se, except that you did not provide enough facts. I cannot understand how the officer had the right to search the trunk. That could have been illegal. The ticket itself, once you are past the search and seizure, 4th Amendment issue, would not be illegal if your son was under 21 years of age. Since the alcohol was unopened and in the trunk, though, this is a case he should most definitely fight. I think even a dismissal would be reasonable, but an infraction for disturbing the peace, at most.

Legal? If he was cited to court, meaning arrested and charged with a crime, then the proper questions are, can any evidence obtained in a search or confession be used against you, and can you be convicted, and what can you do? Hell get the answer to his legal question from the court in response to evidence suppression or other motions, if appropriate. If he consented instead of objecting to the search, then he waived his improper search claims. Whether the charge of minor in possession is valid will also be answered through the process. Effective plea-bargaining could possibly keep the penalties down to modest fines, instead of jail and loss of license. He can go to trial if it can't be resolved with motions or a plea bargain. If you don't know how to do these things effectively, then hire an attorney that does, who will try to get a dismissal, diversion, reduction or other decent outcome through plea bargain, or take it to trial if appropriate. If serious about hiring counsel to help you in this, and if this is in SoCal courts, feel free to contact me. Ill be happy to help use whatever defenses there may be.

No, what was illegal was your underage son possessing alcohol. However, this type of charge is rather minor these days, and a skilled attorney has a good chance of having the case dismissed, either outright or earned.

It may have been an illegal search. The cop needs to have a reasonable suspicion that he will find an illegal substance in the car before he can search. If the search was legal your son can be ticketed for Possession by a Minor if he was a minor and if he knew it was there. For more info from an attorney with expertize in the area call.

Assuming your son is under 21, it is illegal for him to possess alcohol, unopened or not.