A drug injection device comprising: - a first element and a second element arranged co-axially along a central axis, the first element and/or the second element being rotationally movable around the central axis and configured to undergo rotational movement relative to each other, said rotational movement being a unidirectional movement in a first rotational direction corresponding to an action performed on or by the drug injection device and representing an amount of drug delivered, or to be delivered, from the drug injection device, - wherein the first element comprises a protrusion configuration comprising a plurality of serially disposed protrusions equally spaced along the first rotational direction of movement, - wherein the second element comprises first and second deflectable transducers (103a/153a, 103b/153b), each of the first and the second deflectable transducer (103a/153a, 103b/153b) being configured for sequentially cooperating with the plurality of protrusions of the first element to become deflected thereby generating an activation signal as the deflectable transducer (103a/153a, 103b/153b) is deflected when travelling past each protrusion, and - a processor electrically connected with the first and second deflectable transducers (103a/153a, 103b/153b) to register generated activation signals from the first and second deflectable transducers (103a/153a, 103b/153b), and being configured to determine, from registered activation signals, an amount of drug delivered or to be delivered from the drug injection device, wherein - the protrusion configuration is so disposed on the first element and the first and second deflectable transducers (103a/153a, 103b/153b) are disposed on the second element so that a second activation signal generated by the second deflectable transducer (103b/153b) is delayed relative to a first activation signal generated by the first deflectable transducer (103a/153a) as the first element and the second element move relative to each other, - wherein the processor is configured to register the first activation signal and the second activation signal and to determine a time delay there between, and - wherein the processor is configured to provide a) a first control action if said time delay is above or equal to a pre-defined value, and b) a second control action if said time delay is below said pre-defined value. - a first element and a second element arranged co-axially along a central axis, the first element and/or the second element being rotationally movable around the central axis and configured to undergo rotational movement relative to each other, said rotational movement being a unidirectional movement in a first rotational direction corresponding to an action performed on or by the drug injection device and representing an amount of drug delivered, or to be delivered, from the drug injection device, - wherein the first element comprises a protrusion configuration comprising a plurality of serially disposed protrusions equally spaced along the first rotational direction of movement, - wherein the second element comprises first and second deflectable transducers (103a/153a, 103b/153b), each of the first and the second deflectable transducer (103a/153a, 103b/153b) being configured for sequentially cooperating with the plurality of protrusions of the first element to become deflected thereby generating an activation signal as the deflectable transducer (103a/153a, 103b/153b) is deflected when travelling past each protrusion, and - a processor electrically connected with the first and second deflectable transducers (103a/153a, 103b/153b) to register generated activation signals from the first and second deflectable transducers (103a/153a, 103b/153b), and being configured to determine, from registered activation signals, an amount of drug delivered or to be delivered from the drug injection device, wherein - the protrusion configuration is so disposed on the first element and the first and second deflectable transducers (103a/153a, 103b/153b) are disposed on the second element so that a second activation signal generated by the second deflectable transducer (103b/153b) is delayed relative to a first activation signal generated by the first deflectable transducer (103a/153a) as the first element and the second element move relative to each other, - wherein the processor is configured to register the first activation signal and the second activation signal and to determine a time delay there between, and - wherein the processor is configured to provide a) a first control action if said time delay is above or equal to a pre-defined value, and b) a second control action if said time delay is below said pre-defined value.