BERLIN: German inventors have devised an interactive beer mat that can tell the barman when it's time for a refill.

The device comprises a small, flat base plate with a traditional cardboard beer mat on top. The plate conceals sensors that react to the weight of the glass, or stein, and movement of the beer mat.

The sensors relay the data to a computer at the bar. Its inventors believe the gadget could also be used as a voting device in pub games.