A medical device includes a printed circuit board-battery assembly, a tape encapsulation assembly wrapped around the PCB-battery assembly, and a second removable tab positioned on a surface of the tape encapsulation assembly. The second removable tab provides an adhesive layer on a surface of the medical device when the second removable tab is removed from the medical device. The PCB includes the electronic circuitry that performs the functionalities of the medical device, including an optical sensor that comprises at least one light source to emit light towards a measurement site of a user and at least one photodetector to receive light returned from the measurement site. The medical device can connect to a host computing device that performs various operations, including, but not limited to, authenticating the medical device, causing measurement values such as blood oxygen saturation (SpO2), pulse rate (PR), and a perfusion index (PI) to be provided.