The U.S. government on Thursday began enforcing restrictions on flavored electronic cigarettes aimed at curbing underage vaping. But some teenagers may be one step ahead of the rules.

Parents, researchers and students warn that some young people have already moved on to a newer kind of vape that isn’t covered by the flavor ban.

These disposable e-cigarettes are sold under brands including Puff Bar, Stig and Fogg in flavors such as pink lemonade, blueberry ice and tropical mango.