An experimental set-up has been developed to carry out in-situ measurements on hydrogen storage materials. It has been used to perform FTIR-ATR measurements on sodium alanate samples during hydrogen desorption and, in parallel, to perform gravimetrical measurements on the same sample. The ATR spectra showed the typical broad Al-H vibrational features, changing according to the phase change the material undergoes during the load cycle. It is shown that the absorbance of the material at these bands and the hydrogen content correspond to each other in a reproducible way. This behavior may be used to measure the hydrogen mass released by an alanate hydrogen reservoir by measuring the optical absorbance at defined wavelengths. In this paper the results of these experiments that may give rise to the realization of a level sensor in future hydrogen storage applications are presented. Copyright (c) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.