We report the proof of concept of a thin film device with a one to one relationship between the H-2 partial pressure and the lateral progression of a visible optical change along a thin film multilayer 70 mm long The device basically consists of a sensing Mg layer with a thickness gradient It exploits the thickness dependence of the hydrogenation thermo dynamics of Pd capped Mg thin films The optical change of the Mg layer during the metal-hydride transition can be detected both in reflection and in transmission This optical sensor allows a continuous measurement of hydrogen partial pressure in the range between 200 and 4000 Pa (C) 2010 Professor T Nejat Veziroglu Published by Elsevier Ltd All rights reserved