Indonesian tsunami early warning system (INATEWS) has been developed and operated after the tsunami struck Aceh in December 2004. The INATEWS is based on relationship model of earthquake and tsunami potential. At the tsunami observation, INATEWS is still experiencing difficulties due to limited buoy stations. Alternative tsunami observations have been investigated using ionospheric TEC data from GPS signal observations. This paper reviews the methods that have been studied and used for tsunami detection using ionosphere total electron content (TEC) from GNSS data.  The method used for detection of tsunami effects on ionospheric TEC is filtering which includes high past filter, band past filter, polynomial filter, detrended TEC in windows 10 minutes and principal component analysis (PCA). TEWS strengthening with TEC GNSS is under development and currently in the real time multi-station TEC estimation  (Figure 1) and TEC real time analysis spectrum from one GNSS station (Figure 2).