The Wi-Fi Leak Detector with tail can detect water in an area where the water level may submerge the sensor itself and damage it. Please see our Help Center article Is the Wi-Fi leak detector waterproof?
With its 4-foot-long tail, which can detect water along its entire length, the sensor itself can be placed away from the risk area and still be able to detect a leak. The leak detector will also detect humidity and temperature changes, alerting you to an out of range setting.
Examples of specific areas that would be best to use this device would be by a sump pump or in a hot water heater pan.