This work describes the development of an accurate, low-cost, expandable and wearable health and activity monitoring platform. Wearable monitors used to track physical activity are becoming an increasingly popular and effective way to combat our dangerously sedentary lifestyles. Unfortunately most existing wearable solutions are either costly, inaccurate or cumbersome. The goal of this research was to design and create an activity and health monitor that balances wearability, price, efficiency, functionality and accuracy in order to create the most useful device. The development of a custom hardware platform, specialized firmware and a unique iOS application framework enabled the creation of a complete system capable of being used in various applications. The use of a limited number of highly integrated components, miniaturized PCBs and a modular system design led to the creation of thin, dime-sized main board weighing just 9.5 grams and costing less than $25, which can be easily integrated into an article of clothing. Specialized firmware enables this main board to interface with a variety of sensors, both analog and digital, providing accurate data collection and wireless BLE connectivity for at least 100 hours of continuous use in any mode. Initial results show that the system is capable of gathering, transmitting and displaying highly accurate data about the users heart rate, number of steps taken, distance traveled on foot.