E-Stim

Electrostimulation produces a sensation that is not stronger than vibration so much as entirely unlike it.
It reads as a pulse, a tightening or a flutter depending on the setting, and most people need a session or two before it resolves into something they can place.
Two rules that are not negotiable: nothing above the waist, and nothing at all for anyone with a pacemaker or a heart condition. Begin at the lowest setting on every device, every time.