The present invention relates to an aerosol-generating device that is configured for generating an inhalable aerosol by heating an aerosol-forming substrate. The device comprises a device housing for receiving the aerosol-forming substrate and a pyrometer for determining a temperature of a heated target surface within the device housing. The invention further relates to an aerosol-generating system comprising such an aerosol-generating device and an aerosol-generating article for use with the device including an aerosol-forming substrate.