: A sensor for remote detection of formaldehyde (FA) fumes in the atmosphere has been developed, based on the redox reaction between FA and silver nitrate. The sensor is worn as a bracelet and the data acquired are transferred via a Blue-tooth channel to a smartphone. A dedicated software transforms the signal from a grey to a colour scale. The signal response has been assessed over low (20 to 120 ppb) as well as higher (1-15 ppm range) levels. The sensor has been applied to monitor potential FA fumes of some artwork in two locations: the Tate’s gallery in London, during the display of several pieces of Damien Hirst, as well as in the Summer Palace in Beijing. In the first case, one of Hirst’s main subjects is the setting-up of giant fish tanks filled by thousands of liters of FA, in which intact biological specimens are immersed, such as zebras, cows, calves, even sharks. The parallelepiped-shaped basins are then covered with a lid and fully sealed with silicon gums. It has been found that the tanks are surrounded by FA fumes, constantly exuded in the atmosphere (likely via the sealant), reaching levels of 5 ppm, one order of magnitude higher than the 0.5 ppm limit set up by legislation. In the Summer Palace too posters in display and wooden beam works have been found to release FA vapours.