Monnit wireless voltage meters are capable of measuring the voltage of another device, battery, or sensor. Examples of interfacing devices include, but are not limited to: Strain Gauge, Pressure Transducer, RTD, Thermistor, or Thermocouple, Piezo Electric sensors, Photoresistor, Industrial Accelerometer, any kind of variable resistor, any kind of sensor that outputs a voltage, etc. If the device being measured is passive, the user must supply their own excitation voltage, as the Monnit sensor is really just a "voltage observer".