The first of a planned network of tsunami early warning buoys is being laid in the Indian Ocean.
The buoy uses satellite technology to send out warnings
The buoy is being placed between Thailand and Sri Lanka, two of the countries worst-hit by the 2004 tsunami which killed more than 200,000 people.
The buoy, provided by the US, is able to detect sudden increases in pressure deep under the sea and give coastal communities early warning of a tsunami.
The US already operates a similar system in the Pacific Ocean.
The cost of the US-designed device is being shared by the US and Thailand.
A Thai Navy ship carrying it sailed from the holiday island of Phuket, which was badly hit by the Asian tsunami.
It will be anchored about 1,000 km (620 miles) off the west coast of Thailand, near the Nicobar islands.
It is hoped that eventually a network of 24 buoys will extend to Indonesia and Australia, along the deep and unstable fault-line that caused the 2004 earthquake.
"Two years ago, few people really knew what a tsunami was or how powerful and destructive a tsunami could be," US Ambassador to Thailand Ralph Boyce said ahead of the buoy-laying mission.
"There were no warning systems then, and most people did not know what to do when they watched the waters recede from the beaches before the waves struck.
"With the launching of this buoy, we are taking a big step forwards in better protecting hundreds of millions of people living across the Indian Ocean," he added.
But the BBC's South-East Asia correspondent Jonathan Head says that system will only be effective if there are proper warning sirens installed in coastal communities - so far only a few have them.
A smaller tsunami in July this year killed more than 600 people on the Indonesian island of Java, even though there were warnings from Pacific-based monitors.
According to our correspondent the government was unable to pass those warnings on to small villages along the south coast of Java.
The Deep-Ocean Assessment and Reporting of Tsunamis (DART) system has a platform that lies on the seafloor monitoring seismic activity and sending signals to a buoy floating on the surface.
The buoy then uses satellite communication to pass on the gathered information to tsunami warning centres around the Indian Ocean.
In the event of an earthquake it is designed to detect whether a tsunami will occur and pinpoint its height, location and when it will make landfall.