Floods and landslides often hit disaster-prone areas in districts of Indonesia, causing casualties, damage to housing units, and damage to fields and plantations. National Disaster Management Agency calls for increased preparedness. One of them by doing technology-based disaster mitigation. Geofencing plays a vital role in implementing several disaster management mitigation strategies. Previous studies have used geofencing in administration, finance, and security. We conducted this research to apply the haversine formula in disaster management mitigation using geofencing in a district in Indonesia. By utilizing GPS technology, the signal of a cellular device can be tracked or monitored. If an object with a cellular device approaches or enters the geofence area, it will automatically receive a notification that it is approaching or in a disaster-prone area. We carried out this research in several stages. These stages collect data from a list of disaster-prone regions in the West Bandung Regency, analyze software requirements, and conduct software development, including testing. We recorded the latitude and longitude of each area to provide a virtual fence to establish that the area is a disaster-prone area. All of this will result in a system that can monitor people who approach or enter the geofence area, calculate the distance between the object and the center point of the geofence area and send notifications about it with high accuracy. However, this system only can use with the Android operating system. We suggest developing this system, so Android and iOS operating systems can use it.