In known pacifier thermometers of the type as defined hereinabove the temperature sensor comprises a slender measuring probe extending to the front end of the nipple, where it may be held in a guiding element, e.g. as described in U.S. Pat. No. 5,178,466, or the sensor element proper is securely immersed in an encased liquid, e.g. as described in U.S. Pat. No. 5,021,060. In both cases the measuring sensor reacts in a relatively sluggish manner on the supplied heat (warming up the protective or transfer liquid, since the transfer to the measuring sensor needs a certain time, and the body temperature can not be transferred in a perfect manner). In an amended embodiment, the measuring sensor is arranged in a cavity in the inner wall of the nipple in order to reduce the distance to the heat source. However, practice has shown that the transfer of the temperature has not significantly improved.