Disclosed are various systems and methods related to detecting a type of pulse source that is removably attached to a computing device via a data line. The computing device receives two or more pulses from a pulse source via the data line. Based upon the number of pulses received on each input, the computing device can determine the type of pulse source to which it is attached. The computing device further determines an adjustment to the consumption counter based on the identified type of pulse source and the number of received pulses.