A probe, connectable to a machine tool, has an electric generator and a driving element. The electric generator supplies an electric or electronic circuit with electric power, and the driving element is capable of relative rotation with respect to the stator of the electric generator. The driving element is not connected to any external energy source and can be set in rotation simply by activating the rotary axis of the machine tool. The driving element is either rotatably mounted on the probe itself or fixed on the reference table of the machine tool. The probe requires no additional connections to the machine tool on which it is mounted, besides the connection to the rotary spindle, which can be realized with a conventional tool-holder with a standardized tapered shank. The probe is fully compatible with standard probes and can be mounted and used with standard tool-holders without any adaptation.