We present the novel geofencing method in behavioral research, along with its implementation in our free and open-source software Samply for experience sampling research. Geofencing, built on geolocation technology, forms a virtual fence around specific geo-locations. Each time a participant crosses the virtual boundary around the fenced area, an event can be triggered on a smartphone, for example, the participant can be prompted to complete a survey. Geofencing can reduce the problems of continuous location tracking, such as recording sensitive geolocation data and battery depletion. In the scenarios where participants choose their own locations for geofencing (e.g., at home or at work), there is no need to transmit location data to the researcher, so this method can ensure privacy and anonymity. Given the widespread use of smartphones and mobile Internet, geofencing has become a feasible tool for studying human behavior and experience outside the laboratory. The method can advance basic and applied psychological science to a new frontier of contextual research. So far, however, there is a lack of guidance on how and when to use geofencing in research. We describe the current challenges and implementations of geofencing and present three empirical studies in which we evaluated geofencing using Samply. The studies showed that the accuracy and precision of geofencing depend on the type of event, location radius, environment, and operating system. We present potential implications and recommendations for behavioral research.