GPS-technologies have many applications in the field of early warning tasks. All of them have high requirements in terms of accuracy and fast availability of GPS-measurements. A network of new developed Real-Time Reference stations was installed in Indonesia in order to fulfill the high requirement of accuracy for all GPS-based applications of the Indonesian tsunami early warning system. The fast availability of GPS-based measurements is achieved through an automatic near real-time processing of GPS-data. The system processes GPS-data from stations on land (reference stations and GPS-devices at tide gauge stations) and GPS-data from GITEWS buoys, supporting the determination of sea levels at coastline- and offshore-locations. The GPS-based “Ground Tracking System” is a system for an automatic near real-time determination of co-seismic displacements, an important factor for the estimation of a tsunami threat after strong earthquakes. Furthermore, new technologies like GPS-reflectometry are studied which might play an important role for tsunami early warning in the future.