Mr. Mauch and his team developed a weapon that works using radio-frequency identification – the same technology employed in anti-theft tags on clothes in department stores. To fire its gun, you use an accompanying watch. When that watch is activated with a code and sitting on your wrist – or anywhere less than 25 centimetres away from the gun – the gun will fire. Otherwise, it’s a “just a piece of composite,” says Mr. Mauch, and useless as a weapon…

A former long-time colleague of Mr. Mauch’s in the United States, who asked not to be named, called him a “first-rate” weapons designer but said he didn’t appreciate the American context. “The thing that worries me and millions like me is that the anti-gunners in our [government] … ONLY want this technology so they can restrict the rights of law-abiding gun owners,” the colleague wrote in an e-mail. “Would you want to bet your life on your smart phone or laptop? Me neither.”