This book is an exploration of programming in Arduino. The first part of the book helps you get started with Arduino. You will learn what Arduino is, and for what purposes it is used. You are then guided on how to setup the Arduino software on your system. Steps for Windows, Mac OS X, and Linux are given. Sketches, variables, and procedures are discussed, and thus you will know how to use these when programming your Arduino boards. You are guided on how to use the Serial Library and Binary Data in Arduino. You are also guided on how to setup buttons, switches, resistors, and get digital inputs in Arduino. You will also learn how to program these so that they can provide a number of functionalities. A number of Arduino projects are also explored in this book. The book also guides you on how to come up with a keyless door lock system. This is a system which will grant and deny access to users who need to open the door and gain entrance. The user will be required to enter the pin on a keyboard, and this will be compared to the keys stored in EEPROM. This will determine if the user is granted or denied access. You are also guided on how to control access by use of Arduino and RFID (Radio Frequency Identifier Device). In this case, we will not use the keyboard to type the pin, but we will be using the RFID. The following topics are examined in this book: -Getting Started with Arduino -Sketches, Variables, and Procedures -Serial Library and Binary Data -Buttons, Switches, Digital Inputs, and Resistors -Keyless Door Lock System in Arduino -Access Control with RFID and Arduino -Weighing Plate