Looks like the unit is under the whole tile, the graphic is stuck on after tiling, works up to 18mm thickness.
Exactly how they work is probably closely guarded, but it's something projected forward thro' any object up to 18mm thick, including tiles, so Radio wave would be the best guess, something like Radar only more localised and more acurate:
The system overcomes traditional limitations within wet areas of the home, where ugly pull cords, or switches and dimmers placed outside the room have been the norm.
Taptile™ is different. Fixed to the rear of the tile or drywall, the Taptile™ touch sensor projects an array of waterproof and highly sensitive buttons through a thickness of up to 18mm. Each sensor has six buttons which provide three programmable mood light settings plus individual control and dimming of the three active circuits. This enables you to create the desired level of mood lighting whilst in the bath or shower. The front of the tile or drywall is decorated with either self-adhesive artwork (supplied), tile grouting via a stencil, or by adding features such as mosaics, shells or buttons to the surface, creating a seamless, attractive match to the room décor.
The units combine safe extra low voltage (SELV), 100% sealed to industrial standards, with a wireless connection to existing lighting circuits, while meeting all building and safety regulations for both renovations and new build.