Wizard wanted

At the National Theatre last night to see Women Beware Women (or women prefer women as the director said she called it in rehearsals). Three different mobile phones rang during the first act…..so silly, and so distracting, to both audience and performers. Why is it that people can’t think to turn them off before the play starts? I wonder if there isn’t some technology that can be used to ‘blanket’ a theatre auditorium or concert hall with something that removes the ‘phone signal for the duration of the play. Come on you technical wizards: let’s have some simple inexpensive device that theatres can install to let us all enjoy their performances without this kind of interruption.