Tsunamis in the Indian Ocean are rare; this area has not experienced a large-scale tsunami since 1883. No warning system exists for tsunamis in this region.
The US Department of Commerce runs the National Oceanic and Atmospheric Administration which runs a Pacific Warning Center in Hawaii. They maintain an international system of buoys across the Pacific Ocean which acts as an alarm system. The Deep-ocean Assessment and Reporting of Tsunamis (DART) is a part of this larger warning system.
In the 1990’s the United Nation’s International coordination Group for the Tsunami Warning System in the Pacific discussed the danger of tsunamis in both the Indian Ocean and the Caribbean. In September of 1997 they met to discuss extending the warning network to the Indian Ocean, however, no action was taken.
The Pacific Warning Center did monitor the earthquake off Sumatra. They were aware of the danger within 45 minutes of the earthquake. However, no warning was issued to the general population of the region.
(Map Source: NOAA Tsunami Research Program)