SMAKN&reg; DC-DC 0.36" Digital Voltmeter 100V Limit Alarm 2/3 Wires Universal Voltage TesterGreen) *Upper and lower limit setting method: press two keys simultaneously, the red indicator(HV) light, press + or - key to set the desired limit alarm voltage value. And then simultaneously press two keys again, yellow indicator(LV) light, press + or - key to set the desired lower limit alarm voltage value. Then press both keys simultaneously to exit setting. New high-precision digital voltmeter, with upper and lower limit voltage alarm output function. Can be used as overvoltage, undervoltage alarm output. If connect with relay it also can be used as overvoltage or undervoltage protection. 3-wires, and you can change it to 2-wires. Input with anti-reverse protection. When the measured voltage below 10V, automatic transfer decimal point, increase the resolution of low voltage.