A dosage determination device (400, 100) for determining a dosage activity performed by a liquid drug administration device, the dosage determination device (400, 100) being configured to - obtain at least one vibration signal (1101, 1101', 1101") from a vibration determination element, the vibration determination element being configured to obtain the at least one vibration signal (1101, 1101', 1101") in response to registering vibration of the liquid drug administration device, wherein the dosage determination device (400, 100) further comprises one or more processing units configured to - provide a first processed signal by deriving a derivative or a second order derivative on the basis of at least a part of the at least one vibration signal (1101, 1101', 1101"), - determine a number of local extrema in the first processed signal resulting in a number of determined local extrema, and - processing the number of determined local extrema by matching against predetermined patterns of groups of local extrema, each group of predetermined local extrema representing a particular associated dosage activity, thereby determining whether at least one dosage activity is indicated to be present in the at least one vibration signal, and characterized in that the at least one vibration signal (1101, 1101', 1101") comprises a plurality of gyrometer vibration signals and a plurality of accelerometer vibration signals and wherein the one or more processing units are configured to - derive a first combined signal on the basis of the plurality of gyrometer vibration signals, and - derive a second combined signal on the basis of the plurality of accelerometer vibration signals. - obtain at least one vibration signal (1101, 1101', 1101") from a vibration determination element, the vibration determination element being configured to obtain the at least one vibration signal (1101, 1101', 1101") in response to registering vibration of the liquid drug administration device, wherein the dosage determination device (400, 100) further comprises one or more processing units configured to - provide a first processed signal by deriving a derivative or a second order derivative on the basis of at least a part of the at least one vibration signal (1101, 1101', 1101"), - determine a number of local extrema in the first processed signal resulting in a number of determined local extrema, and - processing the number of determined local extrema by matching against predetermined patterns of groups of local extrema, each group of predetermined local extrema representing a particular associated dosage activity, thereby determining whether at least one dosage activity is indicated to be present in the at least one vibration signal, and - provide a first processed signal by deriving a derivative or a second order derivative on the basis of at least a part of the at least one vibration signal (1101, 1101', 1101"), - determine a number of local extrema in the first processed signal resulting in a number of determined local extrema, and - processing the number of determined local extrema by matching against predetermined patterns of groups of local extrema, each group of predetermined local extrema representing a particular associated dosage activity, thereby determining whether at least one dosage activity is indicated to be present in the at least one vibration signal, and characterized in that the at least one vibration signal (1101, 1101', 1101") comprises a plurality of gyrometer vibration signals and a plurality of accelerometer vibration signals and wherein the one or more processing units are configured to - derive a first combined signal on the basis of the plurality of gyrometer vibration signals, and - derive a second combined signal on the basis of the plurality of accelerometer vibration signals. - derive a first combined signal on the basis of the plurality of gyrometer vibration signals, and - derive a second combined signal on the basis of the plurality of accelerometer vibration signals.