Device for detecting a pressure force exerted by a human muscle. If a sensor measures that a defined force is exceeded, a signal is emitted. This signal is used to indicate to the relevant person that he needs to modify his behavior. To determine the teaching effect of this signal, it is proposed for these signals to be stored in a memory and for the stored values to read out after a certain time and compared with more recent signals. The device can be used, inter alia, in a writing instrument which measures both the gripping force on the writing instrument and the writing pressure.