Editing Alcohol Sensor Based on Gas-Sensitive Resistive Materials (section)

== Results ==

=== Sensitivity and Concentration–Response ===
The experimental results show that the MQ-3-based system had a clear and repeatable response to alcohol vapor. After warm-up, the baseline output usually remained around 15–20 in clean air. A representative stabilized baseline is shown in Figure 3. Once the alcohol wipe was introduced, the displayed value in many trials increased rapidly to the range of approximately 40–60, indicating a strong response to the presence of ethanol vapor. This behavior is consistent with the working mechanism of the MQ-3 sensor, in which alcohol exposure increases the conductivity of the sensing layer and produces a larger output signal.

[[File:Figure3.png|thumb|center|500px|Figure 3. Representative baseline signal after sensor warm-up, showing a relatively stable initial reading in the range of about 15–20 before alcohol exposure]]

Although the displayed value was written in a percentage-like format, it should not be interpreted as the exact alcohol concentration. In this system, the signal shown on the LCD was a scaled ADC reading used to visualize relative changes and to trigger an alarm when the threshold was exceeded. This design is appropriate for a warning-oriented device, whose main purpose is to determine whether alcohol exposure has risen above a practical limit rather than to perform rigorous quantitative concentration measurement.

From the perspective of concentration–response behavior, the screenshots support a clear qualitative conclusion: higher local alcohol exposure produced higher sensor output. Even without converting the readings into calibrated ppm values, the experiments clearly demonstrate that the system was sufficiently sensitive to distinguish between background air and alcohol-rich conditions. Therefore, for the intended application of alcohol over-threshold warning, the sensor showed adequate practical sensitivity.

=== Dynamic Response Analysis ===
The Serial Plotter screenshots show that the system responded quickly after alcohol exposure. In the representative curves, the signal typically remained near the baseline for a period of time and then rose sharply once ethanol vapor reached the sensor. Figure 4(a) shows a typical rapid response at short distance, whereas Figure 4(b) shows the subsequent gradual decay. In several cases, the displayed value increased from around 15–20 to above 45 within only a short sequence of plotted points, indicating a fast practical response.

[[File:Figure4.png|thumb|center|500px|Figure 4. Representative dynamic behavior at 0 cm: (a) rapid signal rise after alcohol exposure; (b) gradual recovery after the response peak.]]

The recovery process was generally slower than the rising process. After the peak value was reached, the signal tended to decay more gradually, often with an extended tail instead of an immediate return to baseline. This is physically reasonable for a metal-oxide gas sensor because recovery depends on ethanol removal, desorption, and re-establishment of the surface equilibrium on the sensing layer.

Another dynamic feature visible in the plots is the presence of fluctuations and occasional secondary peaks after the initial response. These features suggest that the alcohol vapor inside the chamber was not perfectly uniform. Instead, the signal was likely affected by transient vapor transport, local mixing, and residual alcohol remaining in the chamber after the wipe had been introduced or moved. Overall, the dynamic measurements indicate that the system is suitable for real-time alarm applications, where practical threshold detection is more important than highly precise dynamic fitting.

=== Effect of Distance in a Closed Environment ===
The influence of distance was investigated by placing the alcohol wipe at 0 cm, 5 cm, 10 cm, and 15 cm from the sensing device inside the closed chamber. Representative response curves are compared in Figure 5. The screenshots show that the sensor produced clear responses at all four tested distances. This means that, within the enclosed experimental volume, ethanol vapor could still diffuse to the MQ-3 sensor and be detected effectively even when the source was not placed immediately adjacent to it. From a practical viewpoint, this is an encouraging result because it demonstrates that the alarm system remained functional across the whole tested range.

[[File:Figure5.png|thumb|center|500px|Figure 5. Representative sensor output curves obtained at different alcohol-source distances in the closed chamber: (a) 0 cm, (b) 5 cm, (c) 10 cm, and (d) 15 cm.]]

However, the effect of distance did not appear as a strictly monotonic decrease in peak value. In some trials, the 10 cm or 15 cm curves still reached relatively high displayed values. Therefore, the most reliable conclusion is not that the peak output simply decreased linearly with distance, but rather that distance influenced the response profile, including the onset of the signal, the steepness of the rise, and the stability of the curve. In general, the 0 cm and 5 cm measurements showed faster and more direct responses, while the 10 cm and 15 cm measurements more often showed delayed rises, broader peaks, or stronger fluctuations.

This behavior can be explained by the closed measurement environment. Inside a confined chamber, ethanol vapor does not travel only along a direct line from source to sensor. Instead, it diffuses, accumulates, and redistributes throughout the chamber volume. As a result, distance still matters, but its effect is coupled with vapor mixing and temporary accumulation. In our setup, distance should therefore be understood as one important factor among several transport-related influences, rather than the sole determinant of signal amplitude.

From these observations, two practical conclusions can be drawn. First, placing the alcohol source closer to the sensor generally leads to a faster and more typical alarm response. Second, because the chamber allows vapor accumulation, the system is still able to detect alcohol reliably even at 15 cm. This means the prototype has useful alarm capability within a finite enclosed space, but it also means that comparative measurements should keep the chamber geometry, source position, and test conditions as consistent as possible if better reproducibility is desired.