MQ-3 Alcohol Gas Sensor
Alcohol vapor sensor for breathalyzer-style projects and safety applications.
Tuned specifically for detecting alcohol vapor concentration, frequently used in breathalyzer-style hobby projects. The MQ-3 is a metal-oxide semiconductor gas sensor whose surface resistance changes in the presence of ethanol vapor, producing an analog output that increases with alcohol concentration — like other MQ-series sensors it needs a warm-up period and isn't lab-calibrated, so it's best suited for relative/comparative alcohol-detection demos rather than legally-relevant breathalyzer readings.
Specifications
| Sensor type | MQ-3 metal-oxide semiconductor (MOS) gas sensor, tuned for alcohol vapor |
| Operating voltage | 5V DC (heater circuit + sensing circuit both typically run at 5V) |
| Detection range | ~0.05-10 mg/L alcohol vapor concentration |
| Warm-up time | Requires several minutes (some sources recommend 24-48 hours for first-use burn-in) of heater warm-up before stable readings |
| Output | Analog voltage proportional to alcohol vapor concentration, plus a digital threshold output (DO) on breakout modules with an onboard comparator |
| Sensitivity adjustment | Onboard potentiometer sets the digital-output trigger threshold |
| Interface | 1 analog pin (AO) + 1 digital pin (DO, breakout-dependent) |
Pinout
| Pin | Name | Description |
|---|---|---|
| 1 | VCC | Power, 5V DC (powers both the internal heater and sensing circuit) |
| 2 | GND | Ground |
| 3 | AO | Analog output — voltage proportional to alcohol vapor concentration |
| 4 | DO | Digital output — threshold-triggered HIGH/LOW based on the onboard potentiometer setting |
Like all MQ-series sensors, allow several minutes of warm-up after power-on before trusting readings, since the internal heater element needs time to reach a stable operating temperature; results also drift with humidity and temperature, so treat readings as relative/comparative rather than a precisely calibrated measurement, and never rely on this sensor for legal or medical breath-alcohol determinations.
Variants
The MQ-3 is specifically calibrated for alcohol vapor and is the right choice for breathalyzer-style demo projects; for general indoor air quality monitoring or gas leak/smoke detection, the MQ-135 or MQ-2 are the more appropriate MQ-series alternatives respectively.
| Variant | Temp range | Hum range | Accuracy | Protocol | Price |
|---|---|---|---|---|---|
| MQ-3 breakout | ~$1-3 | ||||
| MQ-135 | ~$1-3 | ||||
| MQ-2 | ~$1-3 |