A flow sensor system comprising: a durable portion comprising an outer housing having a first opening to receive an injection device, and a second opening at an opposite end to receive a semi-disposable potion; a durable portion electrical connector; a memory; a battery; a processor for receiving and processing signals received from the semi-disposable portion, and for driving the wireless transceiver to send and receive communication signals from the remote device; a semi-disposable portion comprising: a first end having a cannula adapted to pierce a septum of the injection device and a female thread adapted to engage a male thread feature of the injection device; a second end opposite the first end having a male pen needle thread and septum adapted to receive a pen needle; a printed circuit board having mounted thereon a flow sensor chip; a manifold in fluid communication with the cannula and the septum, the manifold comprising a continuous flow channel extending from the first end cannula to a chamber adjacent the second end septum, the flow channel comprising an opening to receive a sensor; and a semi-disposable portion electrical connector for electrical connection to the durable portion electrical connector; wherein the flow sensor chip comprises a sensing surface adapted to be received in the flow channel opening and exposed within the flow channel; the sensor surface having a heating element and at least one sensing element downstream of the heating element. a durable portion comprising an outer housing having a first opening to receive an injection device, and a second opening at an opposite end to receive a semi-disposable potion; a durable portion electrical connector; a memory; a battery; a processor for receiving and processing signals received from the semi-disposable portion, and for driving the wireless transceiver to send and receive communication signals from the remote device; an outer housing having a first opening to receive an injection device, and a second opening at an opposite end to receive a semi-disposable potion; a durable portion electrical connector; a memory; a battery; a processor for receiving and processing signals received from the semi-disposable portion, and for driving the wireless transceiver to send and receive communication signals from the remote device; a semi-disposable portion comprising: a first end having a cannula adapted to pierce a septum of the injection device and a female thread adapted to engage a male thread feature of the injection device; a second end opposite the first end having a male pen needle thread and septum adapted to receive a pen needle; a printed circuit board having mounted thereon a flow sensor chip; a manifold in fluid communication with the cannula and the septum, the manifold comprising a continuous flow channel extending from the first end cannula to a chamber adjacent the second end septum, the flow channel comprising an opening to receive a sensor; and a semi-disposable portion electrical connector for electrical connection to the durable portion electrical connector; a first end having a cannula adapted to pierce a septum of the injection device and a female thread adapted to engage a male thread feature of the injection device; a second end opposite the first end having a male pen needle thread and septum adapted to receive a pen needle; a printed circuit board having mounted thereon a flow sensor chip; a manifold in fluid communication with the cannula and the septum, the manifold comprising a continuous flow channel extending from the first end cannula to a chamber adjacent the second end septum, the flow channel comprising an opening to receive a sensor; and a semi-disposable portion electrical connector for electrical connection to the durable portion electrical connector; wherein the flow sensor chip comprises a sensing surface adapted to be received in the flow channel opening and exposed within the flow channel; the sensor surface having a heating element and at least one sensing element downstream of the heating element.