Embodiments described herein generally relate to devices, systems and methods for measuring a volume or number of doses remaining in a drug delivery device that is used for delivering a dose to a patient. In some embodiments, a dose measurement system for measuring the liquid volume in a container includes a light guide disposed and configured to reflect electromagnetic radiation toward the container. The dose measurement system also includes a light guide disposed and configured to emit electromagnetic radiation into the light guide. A plurality of sensors are located in the apparatus that are optically coupleable to the light guide and are disposed and configured to detect the electromagnetic radiation emitted by at least a portion of the light guide. The apparatus also includes a processing unit configured to receive data representing the portion of the detected electromagnetic radiation from each of the plurality of sensors. The processing unit is further operable to convert the received data into a signature representative of the electromagnetic radiation detected by the plurality of sensors.