The Sound Sensor in Phasmophobia will pick up any sounds made in its area of detection and relay these sound levels back to a monitor in the truck. Placed correctly, one or more sensors can help you track a ghost's movements in an area.
A downside to the Sound Sensors is, of course, that your own team can trigger them. If you have a quiet ghost you won't get much from these - if anything at all. I personally find them to be of little value, however, you should experiment with them yourself and see if they fit your play style. Just don't forget that you'll only get useful information from them if you are watching the monitor in the truck.