A holder (12) for checking non-compliance of a blister package, has a pocket (60) into which the blister package is inserted for carrying out the check. The holder comprises a shallow box (121) with its front face providing the back of the pocket (60). The front of the pocket is provided by a transparent plate (128) spaced from the box and supported by transparent side walls (122,123). The side walls are formed with opposed channels (124) which engage respective marginal edges of a blister package when it is slid downwards to a predetermined position inside the pocket (60). An array of rectangular openings or wells (133) are formed in the front face of the box (121) and are positioned to respectively locate behind the blisters of the blister package when at the predetermined position. Each well contains eight light-sensitive elements (134). Non-compliance occurs when one of the blisters of a used blister package returned by the patient is still in an unopened condition. The sensing elements (134) detect this by ambient light in the pocket not reaching the elements (134) as it is blocked off by an intact region of a friable foil backing strip provided on the blister package. An electrical circuit in the box (121) monitors the elements (134) and provides an output signal indicating that a non- compliance condition exists if a particular blister in the returned package is unopened. Information identifying the position of the unopened blister and the time at which the check occurred is stored in the circuit so that it can be accessed by interrogating the holder. If the ambient illumination is found to be inadequate to produce a clear distinction between compliance and non-compliance, a variable light source (not shown) can be provided to transmit supplementary light into the interior of the pocket by way of the transparent side walls (122,123) and plate (128).L'invention concerne un dispositif de retenue (12) utilisé pour la vérification de la non-conformité d'un emball
