Let us try the following things before proceeding to the next chapter:

• Add an SD card module with the GSM setup. Read the SMS content from the SD card, instead of hard coding it in the sketch. You can utilize the knowledge gained from Chapter 5, Day 3 - Building a Compound Device for using the SD card module.
• Add an HC-SR04 ultrasonic sensor to the GSM setup. Keep the device in your backyard, pointing the ultrasonic sensor away from your house. Write a sketch to send you an SMS every time someone comes within 10 feet of the device. Make it call your phone if someone comes within five feet. You can reuse the knowledge of using the HC-SR04 from Chapter 6, Day 4 - Building a Standalone Device.