Because you set the voltage alarm threshold to above 100mV and below 50mV, when the voltage is detected to be 0, the alarm will be triggered (even if you don't connect anything).
Because you set the voltage alarm threshold above 100mV and below 50mV, the alarm will be triggered when the voltage is detected to be 0 (even if you are not connected to anything).
Because you set the voltage alarm threshold above 100mV and below 50mV, when the voltage is detected to be 0, the alarm will be triggered (even if you don't connect anything).