The catastrophic death toll in Asia due to the tsunami might have been reduced had India and Sri Lanka been part of an international warning system designed to warn coastal communities about deadly waves, experts say.
Some 11,400 people were killed after being hit by walls of water triggered by a earthquake on Sunday morning off Sumatra.
The warning system is designed to alert nations that potentially destructive waves may hit their coastlines within three to 14 hours.
Seismic networks recorded Sunday's massive earthquake, but without wave sensors in the region, there was no way to determine the direction a tsunami would travel.
The international warning system was started in 1965 and is administered by the National Oceanic and Atmospheric Administration.
Member states include all the major Pacific rim nations in North America, Asia and South America, was well as the Pacific islands, Australia and New Zealand, France and Russia.
However, India and Sri Lanka are not members.