The LW water leak detection switch can be utilized in place of a traditional float switch, or electronic wet switch. It has a 5A relay which can be interlocked with any 24V thermostat in the same way a traditional float is, however it provides quicker alarms, a test function, and Wi-Fi app capabilities for alerts to your phone. 

You do not need a pan full of water for this puck to work, it will detect water with a slight presence of water.

The evaporator coils inside of air handlers will produce condensate when it comes in contact with the warm humid air of the space it is conditioning. 

The condensate is drained to the outdoors, however, if the main drain fails, precautions are taken to make sure the water is not discharged in areas that can cause water damage to property and home. 

If your air handling unit is in a location that water leakage would cause damage, it is required to have a secondary pan located underneath the air handler that the overflow condensate will leak into. 

If the secondary pan fills with water, a "float switch" is typically installed, which is a switch triggered by a buoyant float that is pushed up from the water filling the pan. This movement pushes a switch open, that is tied into the thermostat wiring, and it shuts down the unit. 

The LW switch is a modern alternative to this product with 21st century connectivity and reliability.