The “Braun Bell Mug” helps visually-impaired people pour a drink to a desired level without overspill, or having to dip their fingers into the mug to determine how full it is. Three buttons on the handle of the mug are linked to three sensors inside the mug that detect how far it has been filled.
Simply press the button corresponding to the level of liquid you would like and pour away. An alert then sounds when that level has been reached.
Great user centred Product Design.
More info here.