The Supreme Court on Monday questioned the rationale behind a Massachusetts law barring stun guns. In an unsigned order, the eight-member court ruled that the Second Amendment and the high court's precedent on the topic were enough to question the legal reasoning behind the top court of Massachusetts backing the prosecution of a woman that they said unlawfully possessed the electric weapon for self-defense.

The decision, for the moment, sets aside last year's ruling from the Judicial Court of Massachusetts, which upheld the law that carries up to 2.5 years in prison. The state's top court had ruled that the US Constitution's framers never envisioned the modern stun-gun device, first patented in 1972. The state court also said that stun guns are not suitable for military use and that it did not matter that state lawmakers had approved the possession of handguns outside the home.

For the moment, the US Supreme Court didn't go so far as to throw out the Massachusetts stun gun law. Nor did the court outright say stun guns are "arms" for Second Amendment purposes. But the decision is a major threat to the five states and the District of Columbia that ban them outright for civilians, and it comes at a time when all types of weapons are being constructed at home via 3D printing technology.

What the US top court did was demand that the Massachusetts top court come up with a better explanation for the law to remain valid, because its reasoning violated US Supreme Court precedent, the justices said. "...The explanation the Massachusetts court offered for upholding the law contradicts this Court's precedent," the court ruled in a two-page order without even hearing the case.

In 2008, the US Supreme Court, in a decision known as Heller (PDF), overturned a District of Columbia statute and ruled that a "ban on handgun possession in the home violates the Second Amendment, as does its prohibition against rendering any lawful firearm in the home operable for the purpose of immediate self-defense." Now, every state allows people to carry weapons of sorts, some with or without permits. Among other things, Heller rejected the proposition that "only those weapons useful in warfare are protected." The US Supreme Court on Monday said the Massachusetts high court's reasoning was flawed because the Second Amendment extends to weapons "not in existence at the time of the founding."

Justice Samuel Alito and Justice Clarence Thomas wrote separately in a concurring opinion and said the state was going too far in prosecuting Jaime Caetano. The state's top court said the woman could have carried a firearm for protection instead. The two justices noted:

The reasoning of the Massachusetts court poses a grave threat to the fundamental right of self-defense. The Su­preme Judicial Court suggested that Caetano could have simply gotten a firearm to defend herself. 470 Mass., at 783, 26 N. E. 3d, at 695. But the right to bear other weap­ons is “no answer” to a ban on the possession of protected arms. Heller, 554 U. S., at 629. Moreover, a weapon is an effective means of self-defense only if one is prepared to use it, and it is presumptuous to tell Caetano she should have been ready to shoot the father of her two young children if she wanted to protect herself. Courts should not be in the business of demanding that citizens use more force for self-defense than they are comfortable wielding.

The District of Columbia and five other states make it unlawful for civilians to possess a stun gun; they are Hawaii, Massachusetts, New Jersey, New York, and Rhode Island.