A device similar to the "TV-zapper" that blocks cell phone signals appears to be in fairly widespread use in many places. Earliest usage was to provide "secure" meeting rooms, and to prevent anyone from inadvertently or intentionally "phoning out" what was going on.

The device now is reportedly in use in many restaurants and concert halls in many countries.

Unfortunately, it has been ruled illegal in the US, under the prohibition against "broadcasting interfering signals" in FCC regulations. I think the regulations need changing.

Under this US rule, in order to shut off cell phones a restaurant has to put up aluminum foil wallpaper and steel doors.

John