In this chapter, we started off by learning how passive infrared sensors are used to detect motion to protect a predefined coverage area from intrusion. We then looked at connecting these to the inputs on our port expander via opto-couplers as we will now use 12V to power the alarm zone circuits.

We then looked at wireless alarm systems that operate on the open 433-MHz band, which is commonly used for security devices. After exploring the possibility of using the legacy 433-Util bit-banging software on our Raspberry Pi to decode the signals transmitted by devices using a simple receiver, we opted to use a paired receiver device that will interface easily with our alarm circuit inputs.

Finally, we created a simple script that will log the changes in our alarm inputs to a text file, which can later be expanded to log exactly what's going on with the system in detail.