DE 20103745 U UPAB: 20020919 NOVELTY - An optical moisture indicator (2) is secured to or inside a surface (1a) of the construction element (1), and forms the seal for a miniature tube (3) inside this element. The open inner end (3a) of the tube extends into the region of the construction element being monitored for moisture. DETAILED DESCRIPTION - The construction element is made at least partly from wood, mineral material and/or insulation material. USE - None given. ADVANTAGE - A cheap device is used to monitor relative humidity levels inside a construction element to ensure that a critical level is not exceeded, above which moisture or mould damage can occur.