Development in the field of sensor technology, hardware miniaturization, ubiquitous computing and connected solutions paved the way for the development of wearables for continuous physiological parameter monitoring. Continuous heart rate monitoring with clinical accuracy using reflectance photoplethysmogram signals from wrist is highly challenging and presents a potential area of research. In this work, we present a wearable device in a wrist watch form factor for heart rate monitoring. The device runs on a low power ARM cortex M4 microcontroller and integrates a BLE (Bluetooth Low energy) module for wireless connectivity. A heart rate computation algorithm using reflectance photoplethysmography and a 3 axes accelerometer for motion artifact removal is presented in the paper. Heart rate computed by the wrist worn device was validated against heart rate measured using Masimo Radical-7 on 256 subjects. The validation study was conducted in a hospital setting for a duration of 1 month, after obtaining the ethics committee approval and informed consent from the subjects. Details of the experimental setup, clinical validation protocol and observations and inferences made from the study are presented. © 2016 IEEE.