This chapter will be a fascinating introduction to the exciting, and sometimes secret world of telephony. Yes, we have all used it, but today we will learn about it! Looking back in time, remember the first day of this ten-day journey. I must say, you have done extremely well to have reached up to this point. So, let us buckle up and get started on yet another adventurous day with our favorite Arduino.

In this chapter, we will learn how to use a GSM module to dial phone numbers and send SMSs. The GSM module is very handy for long range communication in remote places that do not have Wi-Fi connectivity, but have telephone network coverage. The chapter will explain how a sample forest fire early warning system could be built using a simple GSM module.

You will learn about the following topics in this chapter:

• The GSM module
• Basic AT commands
• GSM module interfacing with Arduino
• GSM module sketch for sending SMS messages
• GSM module sketch for dialing phone numbers
• Forest fire early warning system project idea