The invention relates to an active device (100) having variable energy/optical properties, comprising an active system (1, 12) between a protective substrate (2) and a protective cover (3), which is chosen from an essentially inorganic electrochemical system, an optical-valve system, a liquid-crystal system, a gasochromic system, a thermochromic system, means for sealing against liquid water and/or water vapour, a surround (50) made of at least one metal-based part (5a, 5b) on the perimeter of the device, the surround being assembled to the cover and to the substrate by assembly means (61' to 64') forming at least part of the water-vapour sealing means.