In the case of Caetano v. Massachusetts, Jaime Caetano was convicted for possession of a stun gun in violation of Massachusetts law which prohibits private citizens from owning such weapons. She argued that this violated her Second Amendment rights to bear arms for self-defense as she had obtained the weapon to protect herself against an abusive ex-boyfriend. The Supreme Court unanimously vacated and remanded the decision made by the Supreme Judicial Court of Massachusetts, which upheld her conviction on grounds that stun guns were not in common use at the time when Second Amendment was enacted and thus are not protected under it. The U.S Supreme court ruled that this interpretation is inconsistent with their precedent set in District of Columbia v Heller (2008), where they held that Second Amendment extends to all instruments constituting bearable arms, even those not existing at founding era.

In the dissenting opinion for CAETANO v. MASSACHUSETTS, Justice Alito, joined by Justice Thomas, argued that the Massachusetts Supreme Judicial Court's decision to uphold a state law banning stun guns was in direct violation of the Second Amendment. They contended that this ruling contradicted District of Columbia v. Heller (2008), which established an individual's right to possess firearms for self-defense within their home. The justices pointed out that stun guns are less lethal than handguns and therefore should not be banned under any circumstances as they can serve as effective means of self-defense without causing permanent harm or death. Furthermore, they criticized the lower court’s reasoning behind upholding the ban - including arguments about stun guns not being in common use at the time when Second Amendment was enacted and them being dangerous and unusual weapons - stating it was flawed and inconsistent with Heller precedent.