Tsunami is a catastrophic disaster which causes a huge number of victims and destruction of buildings in the affected area as the impact of massive high-speed sea wave sweeping the land. Indonesia is a country which is vulnerable to tsunami attack since it consists of thousands of islands surrounded by the seas and located in the area where active tectonic plates encounter. In the last 25 years, at least six tsunamis attacked Indonesia regions, where the last fatal one happened in Sulawesi island, September 2018. Indonesia government has been aware and prepared the tsunami alert system which sensors are placed on the sea to trigger an alarm if a tsunami happens. The alarm will be pronounced by loudspeakers at some open public areas so the residents can hear and be prepared with the disaster. However, the weakness of the existing system is it cannot be heard by people located far away from those loudspeakers, especially if they are in the buildings. This paper aims to create a system that can extend and deliver tsunami alarm to public buildings using the Internet connection. The system is successfully implemented and installed in the Disaster Management Bureau and some hotels in Bali, Indonesia.