Researchers in Germany have invented a beer mat that knows when a glass is nearly empty and automatically asks for a refill. The disc-shaped mat can be attached to a normal beer mat so that it still soaks up spilt liquid and displays an advertisement. It also contains a pressure sensor and radio transmitter to alert bar staff of the need for a refill. The mat might also be used for games as it contains an accelerometer that senses when it is being waved.