Abstract: The object of the invention is to provide means and method of monitoring target gas content in gas tight membrane enclosing a volume containing an object. The visible gas indicator comprises means for being fastened to a gas tight membrane enclosing a volume containing an object, where the gas indicator comprises a chamber having a transparent window. The chamber is in gas communication with the interior of the volume. The window is arranged outside said volume, and a substrate is arranged inside said chamber and visible from outside said volume, where said substrate changes colours when exposed to a target gas.