This book is about developing projects using the sensor-modules with Arduino Uno, Raspberry Pi and ESP32 microcontroller development systems. More than 40 different sensors types are used in various projects in the book. The book explains in simple terms and with tested and fully working example projects, how to use the sensors in your project. The projects provided in the book include the following: Changing LED brightness RGB LEDs Creating rainbow colours Magic wand Silent door alarm Dark sensor with relay Secret key Magic light cup Decoding commercial IR handsets Controlling TV channels with IT sensors Target shooting detector Shock time duration measurement Ultrasonic reverse parking Toggle lights by clapping hands Playing melody Measuring magnetic field strength Joystick musical instrument Line tracking Displaying temperature Temperature ON/OFF control Mobile phone-based Wi-Fi projects Mobile phone-based Bluetooth projects Sending data to the Cloud The projects have been organized with increasing levels of difficulty. Readers are encouraged to tackle the projects in the order given. A specially prepared sensor kit is available from Elektor. With the help of this hardware, it should be easy and fun to build the projects in this book.