The Fluke 805/ES is an external vibration sensor that is ideal for situations where it is either difficult or impractical to use the 805 Vibration Meter's built-in vibration sensor. The 805/ES Vibration Sensor lets you take measurements in crowded or hard-to-reach locations, behind machine guards or walls, or in places you cannot reach and where it is difficult to apply sufficient manual pressure to the 805 Vibration Meter.