US Patent 11779709 Supplemental device for attachment to an injection device

A supplemental device for attachment to an injection device, the supplemental device having a housing containing at least two electromechanical switches each having an open state and a closed state and a protrusion associated with each switch configured to protrude from the housing so as to contact a rotatable surface of the injection device while the supplemental device is attached to the injection device; and a processor arrangement configured to detect a change in the state of each of the switches; and to determine a direction of rotation of the rotatable surface of the injection device from the detected state changes.