Caetano v. Massachusetts, 577 U.S. 411

Background

Jaime Caetano, a domestic-violence survivor, possessed a stun gun for self-defense after threats from an abusive ex‑boyfriend; police later discovered the device during a shoplifting investigation.
Massachusetts statute (Mass. Gen. Laws ch. 140, § 131J) criminalized possession of electrical stun devices with limited exceptions for law enforcement; Caetano was convicted at bench trial.
The Massachusetts Supreme Judicial Court affirmed, holding stun guns are not protected by the Second Amendment because they were not in common use in 1789 and are "dangerous and unusual."
The U.S. Supreme Court granted certiorari, vacated the state-court judgment, and remanded, finding the state court’s reasoning inconsistent with Supreme Court precedent.
The Court (per curiam) emphasized that the Second Amendment extends to ‘‘bearable arms’’ not in existence at the founding and that analysis must focus on whether a weapon is commonly possessed by law‑abiding citizens for lawful purposes today.

Issues

Issue	Plaintiff's Argument	Defendant's Argument	Held
Whether the Second Amendment protects stun guns	Caetano: stun guns are "bearable arms" used for lawful self‑defense and widely owned today, so they fall within Second Amendment protection	Commonwealth: stun guns are unprotected because they were not in common use at the time of the founding	Stun guns are protected; the state court misapplied Heller by treating founding‑era commonness as dispositive
Whether stun guns are "dangerous and unusual" and therefore bannable	Caetano: stun guns are nonlethal, widely used for self‑defense, and not both dangerous and unusual	Commonwealth: stun guns are dangerous per se and "unusual" as modern inventions not contemplated in 1789	Court rejected state court’s application: the ban requires both dangerous and unusual; the court erred in treating modernity as making a weapon "unusual"
Whether protection is limited to weapons useful in warfare/militia	Caetano: protection is not limited to military‑use weapons; Heller protects arms commonly used by law‑abiding citizens for lawful purposes	Commonwealth: stun guns are not readily adaptable to military use and therefore not protected	Heller rejects limiting protection to militia/military weapons; military utility is not dispositive
Remedy / disposition	Caetano: conviction should be overturned as inconsistent with Second Amendment protections	Commonwealth: conviction should stand under state statute interpretation	Supreme Court vacated the Massachusetts judgment and remanded for proceedings consistent with this opinion

Key Cases Cited

District of Columbia v. Heller, 554 U.S. 570 (individual right to possess weapons for self‑defense; protection extends to arms not in existence at founding)
McDonald v. City of Chicago, 561 U.S. 742 (Second Amendment applies to the States via the Fourteenth Amendment)
United States v. Miller, 307 U.S. 174 (historical discussion of militia arms and ‘‘common use’’ language)
Reno v. American Civil Liberties Union, 521 U.S. 844 (modern technologies can fall within constitutional protections)
Kyllo v. United States, 533 U.S. 27 (constitutional protections apply to modern technologies)