Device for measuring temperatures and rotational speeds of rotating parts, in particular shafts of electric machines such as motors and generators. Marks (2) which change in function of the temperature are placed on a shaft (4). A fixed sensor (1) reacts to the changes of the marks and emits a voltage pulse from which the temperature and the rotational speed can be derived. The marks may consist of liquid stripes (2) or ferrite (13) whose colour or magnetism (e.g. Curie temperature) change at a given temperature. It is also proposed to mount a simple sensor (5, 12) whose position or sensitivity of measurement vary with temperature and which derives the temperature and rotational speed from the arrangement of fixed geometric marks on the shaft. The measurements are made without contact and require only a sensor.