A "smart gun," if you have not yet heard, is a firearm that uses some type of technology -- fingerprint recognition, etc. -- to ensure that it cannot fire unless it is being held by an authorized user. In 2002, New Jersey passed a law saying that once smart handguns become commercially available in the U.S., three years later gun stores won't be allowed to sell anything else.

Now a smart handgun is available in California, in the form of the Armatix iP1, a .22-caliber pistol that can't be fired unless the user is wearing the watch that unlocks it. But since the law's passage the Supreme Court has weighed in on the Second Amendment -- finding it to protect an individual right in Heller and then applying this protection against state governments in McDonald.

Can New Jersey's law survive a court challenge under this new regime? It'll depend on the makeup of the court that hears the challenge, of course -- the SCOTUS decisions thus far have involved sweeping bans on gun ownership and use, rather than just gun-store sales, leaving future judges some wiggle room. But there are signs in Heller that a law like this is not acceptable.

Here's a relevant passage:

[D.C.'s] handgun ban amounts to a prohibition of an entire class of "arms" that is overwhelmingly chosen by American society for that lawful purpose [of self-defense].

...

It is no answer to say ... that it is permissible to ban the possession of handguns so long as the possession of other firearms (i.e., long guns) is allowed. It is enough to note, as we have observed, that the American people have considered the handgun to be the quintessential self-defense weapon. There are many reasons that a citizen may prefer a handgun for home defense: It is easier to store in a location that is readily accessible in an emergency; it cannot easily be redirected or wrestled away by an attacker; it is easier to use for those without the upper-body strength to lift and aim a long gun; it can be pointed at a burglar with one hand while the other hand dials the police. Whatever the reason, handguns are the most popular weapon chosen by Americans for self-defense in the home, and a complete prohibition of their use is invalid.

Similarly, New Jersey's law will ban the sale of every currently popular handgun model -- that is, all handguns now in "common use," to use language Heller quoted elsewhere from an earlier Supreme Court decision -- and there are legitimate self-defense reasons a gun owner might not want to change to this new technology. These include fears of a malfunction in an emergency, as well as the precious seconds that are lost finding and putting on the watch in the middle of the night.

Heller's basic protection of gun ownership for self-defense could pose problems, too. Presumably more smart guns will be available three years from now, but the iP1 is tiny -- .22s do not possess the stopping power one wants in a self-defense firearm. Further, the Armatix's watch alone costs $400, and it provides little extra value for many gun owners, especially those who don't have children and don't plan to store the gun and watch separately to make theft more difficult. There's no telling how much prices will fall in the years ahead, or how easily other gun makers will be able to integrate smart technology into their designs, but this requirement could put self-defense weapons beyond the reach of poorer citizens.

Banning the sale of every handgun currently on the market, simply because a new product has become available, is an aggressive move. Aggressive enough, perhaps, to run afoul of the Second Amendment as the courts now interpret it.

Robert VerBruggen is editor of RealClearPolicy. Twitter: @RAVerBruggen