Supplemental device for attachment to an injection device

A supplemental device comprising:

• an electromechanical switch arrangement having an open state and a closed state, wherein in the open state two electrical contacts of the electromechanical switch arrangement are electrically isolated from each other, and in the closed state the electromechanical switch arrangement provides a conductive path between the two electrical contacts, the electromechanical switch arrangement comprising:
• a main body;
• and
• a first protrusion configured to protrude from the main body such that the protrusion contacts a first surface of an injection device when any number of dose units are dialed into the injection device, wherein the open state or the closed state of the switch arrangement is configured to change, during dose dialing, when a dose dialed into the injection device moves the electromechanical switch arrangement from a one unit dose position to a zero unit dose position;
• and
• a switching member having an open state and a closed state, the switching member comprising a second protrusion configured to contact a flange of the injection device only in the zero unit dose position of the electromechanical switch arrangement.

A system comprising a supplemental device comprising:

• an electromechanical switch arrangement having an open state and a closed state, wherein in the open state two electrical contacts of the electromechanical switch arrangement are electrically isolated from each other, and in the closed state the electromechanical switch arrangement provides a conductive path between the two electrical contacts, the electromechanical switch arrangement comprising:
• a main body;
• and
• a protrusion configured to protrude from the main body such that the protrusion contacts a surface of an attached injection device in a zero unit dose position of the electromechanical switch arrangement, wherein the open state or the closed state of the switch arrangement is configured to change, during dose dialing, when a dose dialed into the attached injection device is moves the electromechanical switch arrangement from a one unit dose position to the zero unit dose position;
• a processor arrangement configured to:
• detect one or more changes in the open state or the closed state of the electromechanical switch arrangement;
• determine from the one or more changes in the open state or the closed state that the dose dialed into the injection device, during dose dialing, has moved from the one unit dose position to zero unit dose position;
• and
• in response to determining from the one or more changes in the open state or the closed state that the dose dialed into the injection device moves the electromechanical switch arrangement from the one unit dose position to the zero unit dose position, change a display output of the supplemental device from a dose delivery display to a dispense-end display, and
• the attached injection device.