This lecture covers the development of low power wearable sensors for monitoring air quality, breath analysis, and environmental exposure. It discusses the importance of wearable sensors in tracking biomarkers and environmental pollutants, highlighting the impact on health, including respiratory infections, cancer, cardiovascular diseases, and diarrhoea. The lecture delves into the history of gas sensors, their diverse applications, and the materials used in their construction. It explores the implementation of gas sensors in everyday devices like smartphones and the challenges faced in industrial adoption. The lecture also examines the principles behind conducting polymer and piezoelectric crystal gas sensors, as well as the use of carbon nanotubes in gas sensing applications.