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

=== 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.