You mean, when is an Open Container not an open container?

When it is a Bottle of wine that is:

a) purchased, along with a meal, by a Restaurant or hotel patron
b) partially consumed by that same patron
c) resealed by the restaurant or hotel, and
d) transported outside of the passenger area of a car

Under Massachusetts law, it is illegal to have any kind of open or unsealed bottle, can, or other receptacle containing an alcoholic beverage in the passenger area of a car.  This prohibition includes partially-consumed bottles of wine resealed by restaurants, which is why you might have heard they are illegal.  However, under the open container statute, which you can read at M.G.L. ch. 90 § 24I, a car’s passenger area does not include the trunk or a locked glove compartment.  So you may legally transport in your trunk a partially-consumed bottle of wine that was resealed by the restaurant you purchased it from to complement your dinner.  Transporting that same resealed wine bottle in your car’s passenger area carries a $100 – $500 fine, just like any other open container containing an alcoholic beverage.