A replaceable unit for an electrophotographic image forming device according to one example embodiment includes a housing having a reservoir for storing toner. A rotatable shaft is positioned within the reservoir and has an axis of rotation. A first magnet and a second magnet are connected to the shaft and rotatable around the axis of rotation in response to rotation of the shaft. The first magnet and the second magnet are detectable by a magnetic sensor when the replaceable unit is installed in the image forming device. A polarity of the first magnet is oriented opposite a polarity of the second magnet relative to the shaft. An amount of angular offset between the first magnet and the second magnet varies depending on an amount of toner in the reservoir.