Detectors and techniques useful with automated acquisition and notification systems

Sensors and techniques for an automated data acquisition and notification system having a plurality of receptacles adapted to store items. In each of the plurality of receptacles, at least one sensor is operated to detect a presence of an item in that receptacle. Light is emitted from a planar surface within the receptacle to a space within the receptacle opposite the planar surface. While that light is emitted light incident on the planar surface is detected. A determination is made whether an amount of light that is detected is significant to indicate a presence of the item.