The ARCoptix Velocimeter is a unique non-contact speed sensor that allows to measure smallest variations in the dynamics of a mechanical watch oscillator during oscillation. The working principle is based on interferometric "self mixing" effect in laser diodes. Light emitted by a laser diode and reflected from a moving object will lead to a modulation within the emitting diode. Such modulations can be detected and used for real time speed measurements. This new principle has high performance and is cost-effective.