They x-ray all luggage going onboard. If they see something that attracts their attention, they'll pull it aside and you'll be required to go down to the 'sin bin' and open it in front of security. Normally, some cruise lines say that if they find it in the original bottle, they will confiscate it and give it back to you the last night of your cruise. However, if it's not in the originally bottle, they will discard it. Some cruise lines say if they find it they will always discard it.
As for whether you'll get caught; sometimes you get lucky and sometimes you don't.
With NCL, you are allowed to bring as much wine or champagne onboard as you want at the initial embarkation port only. However, this must be in your carry-on bags and a $15 corkage fee will be charged to your onboard account for each 750ml bottle. You can read about it here; Frequently Asked Questions