How we change what others think, feel, believe and do
Physically touch the person as you interrupt them.
Keep the touch light and generally aim for the arm or the back, depending on where you are relative to them.
In more intimate situations, you can touch more firmly, for example with a hug.
Be careful about social rules when doing this -- it is possible to unintentionally offend people in any touch situation.
A manager places a hand on the arm of subordinate and says their name to stop them rambling on in a meeting.
A child grabs their mother's clothes to get attention.
A sales person rests a hand on the shoulder of a customer and greets them.
A physical touch is an intimate action and will often cause the other person to pause as you invade their body space uninvited. However, if the touch is light and related to non-threatening action then it may well be permissible.
There are zones of the body that are permissible to touch in different situations. In most cases this includes the arm and the back.
The touch interrupt can be a form of Power Interrupt when it is used to assert authority or superior position.