Methods and compact automatic devices are provided for delivery of micro doses of liquid drugs to a patient. Devices have a fluid supply reservoir comprising an expandable indicator supplied with a sensor, a mechanism forcing the fluid to squeeze predetermined dose out, and a processor treating sensor's signals accordingly to preprogrammed algorithm. The method comprises steps: (a) initiating the delivery cycle, (b) acquiring sensor's signals, (c) treating signals in order to integrate an intensity of output flow and to determine when the squeezing-out force must be terminated, (d) terminating the cycle accordingly to processor's command. Self-testing of devices occurs while each fluid delivery cycle. Their high dosing precision exceeds that of known analogs about two orders of magnitude. A possibility to use low cost disposable exit port assembly and/or easy replaceable factory pre-filled cartridges is an additional advantage eliminating risks of overdosing, air bubbles, and/or compromised sterility.