Electrical impedance detector for measurement of physical quantities, in particular of temperature. The detector comprises electrodes (11,14), between which the electrical impedance (C;R) that represents the physical quantity to be measured is measured. Between these electrodes (11,14) there is an active material whose impedance properties are a function of the physical quantity to be measured. The active material of the detector is a very thin thread-like glass or glass-ceramic fibre (10), which has been manufactured by means of the glass-drawing technique. Further, a process for the manufacture of said detectors is described.