Americans seeking a legal way to jam cell phones can look into passive jamming technologies. For instance, lining your office in lead should ensure that no signals get in or out. But if lead is too industrial to suit your decor, a more genteel alternative exists: You could install magnetic wood paneling throughout. A Japanese scientist, Hideo Oka, has invented a new kind of building material, saturated with magnetic particles made of nickel-zinc ferrite that supposedly deflect 97 percent of mobile-phone signals.

Magnetic wood that silences mobile phones could prevent mobile use in cinemas, restaurants, theatres or anywhere it is installed.

Magnetic wood could be a major plank in the battle against noisy cellphone users. The high-tech material absorbs microwave radio signals, making it impossible to use a mobile phone in any room lined with it. Or a radio for that matter. So theatres and restaurants, for example, can stop people using cellphones on their premises without resorting to signal jammers.