In this work a new device for measuring the parameters of a fog is described. It is developed by our team and is called Fog Detector Indicator 1 (FDI-1). It is a part of a sensor system for control of the parameters of a fog which is used for decontamination of objects polluted by different circumstances. FDI-1 is a custom indication unit used in various systems for evaluation of fog parameters that gives the operator a visual result for the change of the input voltage. The main function of the indicator is to show the measured voltage applied on its coax input. Usually, this measurement can be done with a regular voltmeter, but the nature of the measurement of a fluid (fog) density, droplet diameter or contamination assumes very rapid changes of the measured values and also very short peaks of the maximum and the minimum of the measured variable. FDI-1 is can be used namely in such cases.