Most people treat their Wi-Fi router as a one-way device—it pushes internet into your home, and that's that. But those radio waves bounce around your rooms constantly, and the signals carry more information than you might expect. Open-source projects now show how to tap into that data to monitor your home without buying dedicated sensors.
An ESP32 board—a small microcontroller—and the right software can detect motion, track temperature, measure air quality, and even sense radiation. The trick lies in software that reads information already flowing through the air. Here's what these projects can do, and why they matter for anyone running a smart home on a budget.
Detecting Motion Through Wi-Fi Signals
Wi-Fi signals don't travel in straight lines. They bounce off walls, furniture, and everything else in your home. When someone walks through a room, they change those signal paths. ESPectre is an open-source project that analyzes these changes using Wi-Fi Channel State Information. The board reads how your router's signals are being distorted and converts that into motion and presence data.
Traditional motion sensors need infrared detectors or radar modules. ESPectre needs neither. The Wi-Fi already flooding your home is the detection medium. When integrated with Home Assistant through ESPHome, the system can trigger automations—lights turning on when you enter a hallway—without additional hardware beyond the ESP32.
Adding Radar for Precise Tracking
Wi-Fi CSI handles basic presence detection well. Some projects go further. Connecting an mmWave radar sensor to an ESP32 adds radar-based motion detection that can pick up tiny movements like breathing. Some modules can track multiple targets simultaneously, reporting each target's position, speed, and distance.
With the right setup, you can plot detected targets on a floor plan and watch them move around in near real-time. This level of detail matters for automations that need to know where people are, not just that someone is somewhere in the house.
Seeing Temperature Patterns
A standard temperature sensor tells you the ambient reading in a room. It misses a lot. Windows let in cold patches. Electronics overheat in specific spots. Walls hide temperature differences that show up as mold warnings down the line.
Pairing an ESP32 with an MLX90640 thermal sensor creates a DIY thermal camera. This tiny infrared sensor measures temperature at the pixel level and renders it as a color image. You can scan for cold drafts near windows, spot devices running hot, or map temperature distribution across a room. It's not going to replace a professional thermal imaging tool, but it gives you basic thermal awareness with inexpensive hardware.
Monitoring What You Breathe
Outdoor air pollution gets plenty of attention. Indoor air quality often gets ignored, even though daily habits like cooking or running a 3D printer can release particulates and volatile organic compounds into your living spaces. An ESP32 combined with a sensor like the Sensirion SEN66 monitors CO2 levels, particulate matter, VOCs, and NOx right in your rooms.
With ESPHome integration, the data flows into Home Assistant where you can build a dashboard or set up alerts when readings climb past safe thresholds. If you have older kids, there's an added bonus: alcohol releases VOCs. A spike while you're out could trigger an alert.
Measuring Background Radiation
Your home has background radiation. It's usually nothing dangerous, but you might be surprised by the levels. HAT Geiger is an open-source project that turns an ESP32 into a Geiger counter. Radiation strikes create pulses—the classic clicking sound you hear in movies. The ESP32 counts those clicks and converts them into an estimated dose rate.
Unlike a handheld Geiger counter, you can leave this running non-stop and track how your home's background radiation changes over time. Some level of background radiation is always present; detecting it doesn't mean you need to worry.
Why This Matters for Your Smart Home
These sensors share a common thread: they repurpose cheap, widely available hardware to measure things that usually require expensive dedicated devices. For Home Assistant users, ESPHome makes integration straightforward. Sensor data flows into your existing automations and dashboards without needing yet another cloud service.
The real appeal is customization. Commercial sensors lock you into their capabilities and their app. A DIY approach means you decide what to measure, where to place sensors, and how to use the data. Your motion data, thermal readings, and air quality measurements stay on your own server—no third-party cloud required.
At a Glance
- ESP32 boards can run multiple sensor types without expensive dedicated hardware
- ESPectre detects motion using Wi-Fi signal changes—no PIR or radar needed
- MmWave sensors add precise tracking with position and speed data
- MLX90640 thermal cameras reveal temperature patterns invisible to standard sensors
- Air quality sensors monitor CO2, VOCs, and particulates with ESPHome integration
- HAT Geiger measures background radiation levels over time
Our Analysis
These projects sit at an interesting intersection: they're accessible enough for beginners who can follow a tutorial, but powerful enough to replace commercial products that cost significantly more. The trade-off is configuration time. Commercial sensors work out of the box. DIY sensors require setup—flashing firmware, wiring components, configuring ESPHome entries. That investment pays off in flexibility, cost savings, and data ownership.
Most smart home products collect data and send it elsewhere. ESP32 projects keep everything local. For privacy-conscious users, that's a significant advantage over cloud-dependent alternatives.
The ecosystem keeps growing. New sensor compatibility gets added to ESPHome regularly. Improvements come in software, which means existing boards stay useful as the project evolves.
What to Watch Next
The gap between DIY and commercial sensor capabilities keeps narrowing. Watch for more sensors getting ESPHome support, particularly in environmental monitoring. If you've been waiting for affordable air quality monitoring that doesn't require deep technical knowledge, the tools are already here—and they're getting easier.
Who Should Care
- Home Assistant users looking to expand sensor coverage without cloud dependencies
- Budget-conscious smart home builders who want professional-grade monitoring at DIY prices
- Privacy-focused users who want to keep home data local rather than on third-party servers
- Tinkerers interested in learning how wireless signals carry more than just internet traffic
Key takeaways
- ESP32 boards with appropriate sensors can replace multiple commercial devices at a fraction of the cost
- Wi-Fi CSI motion detection eliminates the need for additional hardware in many use cases
- ESPHome integration makes all of these sensors work smoothly with Home Assistant
- DIY sensors keep data local, addressing privacy concerns that come with cloud-dependent products
- The main cost is setup time, not hardware—the investment pays off in flexibility and control
Frequently asked questions
Do I need programming experience to set up these ESP32 sensor projects?
Basic familiarity with flashing firmware and editing configuration files helps, but ESPHome handles most of the complexity. Step-by-step guides exist for each sensor type.
How accurate is Wi-Fi CSI motion detection compared to PIR sensors?
ESPectre can detect presence more consistently than basic PIR sensors, especially in scenarios where someone is sitting still—PIR often misses this, but Wi-Fi signal changes don't.
Can I run multiple sensor types on a single ESP32 board?
Yes, as long as the sensors use compatible communication protocols (I2C and UART are common). You can combine temperature and air quality sensing on one board.
Is the radiation monitoring actually useful for home use?
Most homes have background radiation at safe, unremarkable levels. The HAT Geiger project satisfies curiosity more than practical safety needs, but it demonstrates what ESP32 boards are capable of measuring.
What's the total cost for a basic multi-sensor setup?
An ESP32 board costs a few dollars. Sensors vary in price depending on type. A complete setup covering motion, temperature, and air quality costs significantly less than commercial alternatives for similar capabilities.