The beer mat detects the fill of the bottle or a glass and translates that to an optical feedback. A full drink the base shines blue. The more you drink the greener it gets. The drink is also lighted what looks preety cool.
The direct translation of the amount of drinking in a colour really influences the drinking behaviour. Sometimes people take an extra big pull to see a big jump of the colour. The beer mat is also a preety good drink reminder. It's hard to not keep on drinking when the drink is shining so nicely.
A very nice effect is also that it the lighing reduces the risk to spill the drink when it's dark.