A geo-fence is a virtual border or fence that surrounds a physical site. It forms a barrier between that site and the surrounding environment like the real fence. Unlike a physical fence, Geo-Fencing with NodeMCU ESP8266 can detect movement within the virtual fence. It can be any size or shape. Geofences are built with mapping software, which allows the user to build the geo-fence across the chosen geographic region. It is composed of a set of coordinates, such as latitude and longitude, or, in the case of a circular geofence, one point that serves as the center and radius.