Detecting events or changes in machines, equipment or environment is becoming highly critical. Such equipment needs reliable, robust and accurate sensors in order to avert risks that could endanger human lives, environment etc. This book discusses the theories and concepts of sensors. Most of the topics introduced herein cover new technologies and applications of sensors. The various studies that are constantly contributing towards advancing technologies and evolution of this field are examined in detail. The extensive content of this book provides the readers with a thorough understanding of working of sensors and its application.