Various embodiments of a "smart" drug delivery pen are provided which include a drug delivery pen having an inertial sensor or accelerometer 276. A system is also provided that includes the smart drug pen in conjunction with a data management unit(s) DMU. The drug delivery pen also includes a momentary micro-switch 267 wherein depressing the injection knob 204 activates the momentary switch for waking up the device from sleep mode. Moreover, the duration of actuation of the micro-switch provides an indication whether the dose has been accurately delivered