A Japanese electronics company has developed drinking glasses which signal when they are almost empty so that table staff know when to bring a refill.

The technology is an adaptation of the tagging systems used to try to stop people stealing from shops.

A microchip and a coil in the base of each glass interact with a coating on the surface of the vessel to work out how full it is and then signal this information to a base station.

The glasses, described in New Scientist magazine, were developed by a team at the Mitsubishi Electric Research Laboratories in Cambridge, Massachusetts, US.

Dishwasher safe

The coating on each glass conducts electricity and makes the glass behave like a capacitor, an electrical device that stores charge.

As the drinker drinks, less of the glass is in contact with the liquid inside and the capacitance of the glass falls.

A microchip in the base of the dishwasher safe glass reads this change and uses a coil to signal when the level has fallen far enough to assume that the drinker might be ready for a refill.

A code in the chip identifies each individual glass and could be used to signal to mobile devices carried by table staff or a central display behind a bar.