The monitoring of conditions within a building, including the temperature, humidity, and CO₂ levels is becoming increasingly more common, with the goal being to adjust heating, cooling, and ventilation systems to keep the occupants of the building as comfortable as possible. In this chapter, such a system is explored and implemented. The following topics will be covered:

• Creating complex firmware for the ESP8266
• Integrating an MCU into an IP-based network
• Adding CO₂ and I2C-based sensors
• Using GPIO and PWM to control relays and DC voltage-controlled fans
• Connecting networked nodes using a central controller