Reverse-Engineering a (Hawk) Tuya-Based Air Quality Monitor

I received a (Hawk) Tuya-compatible air quality monitor as a Christmas gift in 2024. After integrating it with Home Assistant to automate my air purification system and log data, I noticed suspiciously regular ~1-hour patterns in the CO₂ readings. This prompted a deeper investigation into the monitor’s actual capabilities.

Overview

This write-up documents an investigation into a (Hawk) Tuya-compatible air quality monitor purchased from Amazon. The device claims to measure carbon dioxide (CO₂), volatile organic compounds (VOCs), temperature, and humidity. However, through targeted testing and data analysis, it became clear that the device does not contain a true CO₂ sensor and instead derives CO₂ values from VOC readings.

The monitor in question is widely available under various brand names and claims to use an NDIR sensor to measure CO₂. Suspicion was raised due to consistent and regular ~1-hour oscillations in the CO₂ data, even when the room was unoccupied and the HVAC system was inactive or cycling at different intervals.

Testing Procedure

Figure 1: CO₂ and VOC levels logged during a controlled breath test. VOC and CO₂ spiked simultaneously, suggesting the CO₂ reading is derived from VOC data.

• Data from the air quality monitor was logged over several days, revealing artificial patterns in CO₂ measurements.
• Since my breath can often knock a buzzard off a manure truck, I directed a sample at the sensor. While the monitor didn’t melt as expected, it did register a sharp spike in both VOC and CO₂ levels.
• A correlation analysis was conducted between VOC and CO₂ readings using this test data.

Figure 2: A strong linear correlation between VOC and CO₂ values confirms that CO₂ is algorithmically estimated from VOC.

Figure 3: Polynomial regression shows that a cubic model fits the VOC-to-CO₂ relationship best, supporting the idea of a predefined internal mapping.

Findings

• Strong correlation: R² ≈ 0.96 between VOC and CO₂ values, indicating that the device uses an internal algorithm to estimate CO₂ from VOC.
• Cubic model fit: Polynomial regression revealed that a cubic model best fits the VOC-to-CO₂ relationship, confirming algorithmic derivation.
• Misleading labeling: The "CO₂ sensor" label is deceptive; the device functions more like a breathalyzer or general VOC detector.

Conclusion

This (Hawk) Tuya-compatible air quality monitor does not measure CO₂ directly, despite advertising to the contrary. Instead, it infers CO₂ levels from VOC data, leading to artificial patterns and misleading readings. While the VOC sensor itself appears to function consistently, the CO₂ output is not trustworthy for environmental or pattern analysis.

Takeaway

Consumers should be cautious of low-cost air quality monitors, especially those that promise broad functionality at suspiciously low prices. Claims of NDIR sensors should be verified through third-party reviews, teardowns, or data testing.

Also, shame on Amazon for selling this cheap, deceptively-labeled garbage. The company could put a stop to this but they look the other way because... money.

Next Steps

In the future, I might test additional VOC sources, compare the readings with a real NDIR sensor, or build a custom logger with a transparent and accurate sensing component.