CNIL: details on devices for audience measurement

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Audience and attendance Measurement in public spaces


More and more companies are using devices that collect data from mobile devices (mobile phones, smartphones, etc.), to measure the audience of billboards or attendance to publicly accessible areas.

The CNIL has reiterated that the rules are applicable to these devices in order to respect the privacy of the persons concerned.


Indeed, the CNIL has mentioned that these devices used to measure audience or attendance require special attention, insofar as they collect location data of people, they can be particularly intrusive.

Strong guarantees must therefore be provided to people. According to the CNIL these processing activities can be:

  • Based on the legitimate interest associated with strong pseudonymisation measures,
  • Based on the legitimate interest associated with anonymisation measures at short notice,
  • Based on free, specific and informed consent prior to data collection.

Under current legislation, an authorisation from the CNIL is necessary only in the following cases:

  • The device is installed on a public or private road opened to public traffic: on a billboard installed in the street for example;
  • The device is not installed on the public road but is visible from a public road, for example, a device installed in a sports arena but visible from the street;
  • The device is installed in a room mainly used as an advertising medium: in a separate window of the sales area.

Moreover, insofar as these systems consist insystematically monitoring people by means of an innovative technical device, they all require the completion of a Data Protection Impact Assessment prior to their implementation.