Aerosol-generating article having a liquid indicator

An aerosol-generating system comprising:

• an aerosol-generating article including an aerosol-forming substrate and a hydrochromic material, the hydrochromic material configured to be transparent or translucent when in contact with the aerosol-forming substrate and to be opaque in an absence of the aerosol-forming substrate;
• and
• an aerosol-generating device configured to receive the aerosol-generating article, the aerosol-generating device including a power supply, a photosensor, and a controller, the photosensor configured to sense an optical property of the hydrochromic material of the aerosol-generating article, the controller configured to permit a supply of electrical current from the power supply when the optical property indicates that the hydrochromic material is transparent or translucent and to halt the supply of the electrical current from the power supply when the optical property indicates that the hydrochromic material is opaque.