In a per curiam opinion, the Court vacated and remanded a decision by the Supreme Judicial Court of Massachusetts that upheld a state law prohibiting the possession of stun guns after considering "whether a stun gun is the type of weapon contemplated by Congress in 1789 as being protected by the Second Amendment." The Court held that the state court's opinion directly contradicted DISTRICT OF COLUMBIA v. HELLER (2008), in which the Court held "the Second Amendment extends, prima facie, to all instruments that constitute bearable arms, even those that were not in existence at the time of the founding." Alito, joined by Thomas, concurred in the judgment, noting that "[t]he lower court's ill treatment of HELLER cannot stand."
The Court's opinion is here. The concurring opinion by Justice Alito, joined by Justice Thomas, shows the wisdom of Heller: Ms. Caetano, the petitioner in the Supreme Court, was given a stun gun by a friend who wanted her to be able to protect herself from an abusive ex-boyfriend who had already put her in the hospital once. It worked. The next time he menaced her, she pulled out the gun. He thought the better of it and left.