Optical gyroscopes are widely used in vehicle navigation. They use laser beams in a fibre-optic loop, and the beams produce interference when the device's orientation changes. Optical devices are more accurate than their mechanical counterparts, but are hard to miniaturize. Andrey Matsko and his colleagues at OEwaves in Pasadena, California, have made one with a volume of just 15 cubic centimetres. Instead of producing interference in a large fibre-optic loop, the light resonates inside a minuscule crystalline cavity. The gyroscope drifts by only three degrees per hour, an order of magnitude better than previous efforts.