They are suitable for alcohol checker. MQ - 3 gas sensor composed by micro AL2O3 ceramic tube, Tin Dioxide (SnO2) sensitive layer, measuring electrode and heater are fixed into a crust made by plastic and stainless steel net. The heater provides necessary work conditions for work of sensitive components. The enveloped MQ - 3 has 6 pin, 4 of them are used to fetch signals, and other 2 are used for providing heating current. This alcohol sensor is suitable for detecting alcohol concentration on your breath, just like your common breathalyzer. It has a high sensitivity and fast response time. Sensor provides an analog resistive output based on alcohol concentration. The drive circuit is very simple; all it needs is one resistor. A simple interface could be a 0 - 3.3 V ADC. Resistance value of MQ - 3 is difference to various kinds and various concentration gases. So, when using these components, sensitivity adjustment is very necessary. we recommend that you calibrate the detector for 0.4mg / L of Alcohol concentration in air and use value of Load resistance that (RL) about 200 K? (100 K? to 470 K?). When accurately measuring, the proper alarm point for the gas detector should be determined after considering the temperature and humidity influence.