As Laetitia Gros points out at a conference at Orange’s 2021 Research Exhibition, this is in line with a very obvious trend: an increasing number of tools for measuring emotions (EEG or electroencephalographic headsets and watches) are soon to be available on the market. A question mark remains over the relevance of these tools, particularly in relation to the services provided by a telephone carrier. What do they actually measure? Using significant results from Orange’s laboratories, the various approaches for measuring emotional and cognitive states (subjective, physiological and behavioural) are presented. The results underline the complexity of such measurements and the questions they raise.