You already know the basic premise of the effect. Somebody feels that they were physically tapped on the shoulder or touched on some other area of their body whilst you stood a major distance from them. As the audience confirms, you never touched the volunteer of the experiment at any time.
No doubt you are also already aware that, in many other effects of this type, you ultimately do have to touch the volunteer — either yourself or using a gimmick under the cover of misdirection. (Such effects include Steve Banachek Shaw’s Psychokinetic Touches, Lior Manor’s Invisible Touches, Peter Turner’s Midas Touch on the one hand, all the way through to D’Angelo’s Touch and Morgan Strebler’s Touched.)