A medical device for infusing medical substances has activation buttons accessible on the exterior of the device housing. Activation buttons and corresponding electrical switches within the housing are configured to prevent inadvertent activation of the buttons and therefore inadvertent operation of the switches to initiate a process such as medical substance delivery to the user. The device employs overlap of respective time traces initiated by activation of the activation buttons to determine whether activation is intended and valid. These time traces do not have to be initiated simultaneously or in any particular sequence. The activation buttons can be elastomeric overmolded buttons set within cutouts in the housing, and, when depressed, make physical contact with respective switches.
