BANGKOK - In April 2012, Indonesia's Banda Aceh, the city worst hit by the tsunami that killed at least 226,000 people on Boxing Day ten years ago, received a terrifying reminder of how unprepared it was for the next disaster.
As an 8.6-magnitude quake struck at sea, thousands of residents shunned purpose-built shelters and fled by car and motorcycle, clogging streets with traffic. A network of powerful warning sirens stayed silent.
No wave came. But if it had, the damage would have been"worse than 2004, if it was the same magnitude of tsunami", said Harkunti Rahayu, from Indonesia's Bandung Institute of Technology.
As the 10th anniversary of the disaster approaches, experts and officials say weaknesses remain across the region in a system designed to warn people and get them to safety.
For millions in coastal areas, warnings don't always get through, thanks to bureaucratic confusion and geography. In the most vulnerable areas, infrastructure is wanting, and many lack the basic knowledge to keep themselves safe from the deadly waves.
Since the disaster, a sophisticated early warning system has sprouted from next to nothing, costing over US$400 million across 28 countries.
With 101 sea-level gauges, 148 seismometers and nine buoys, the Indian Ocean Tsunami Warning System can send alerts to countries' tsunami warning centres within 10 minutes of a quake, Tony Elliott, the head of the UNESCO secretariat that oversees the system, told Reuters.
But there has also been mismanagement and waste.
In Indonesia, a German-funded detection initiative built an expensive network of buoys - and then scrapped them - after reports of cost overruns and signs they were ineffective.
All but one of nine Indonesian-operated buoys had been lost or damaged by fishermen, said Velly Asvaliantina, an official at Indonesia's Agency for the Assessment and Application of Technology.
The remaining buoy is not operational, she said.
Elliott said technological advances mean the lack of buoys is not a significant impediment in tsunami detection.
"THE LAST MILE"
A far bigger concern is getting warnings to at-risk coastal communities, and making sure people get to safety in time.
In some of the countries worst affected in 2004 - Thailand, Indonesia and India - much progress has been made, officials said. But concerns remain about this final, crucial stage.
The 2012 failure in Aceh prompted a reassessment in Thailand, where 5,395 people died in 2004, said Somsak Khaosuwan, head of Thailand's National Disaster Warning Center. "We put our systems to the test each day. Our warning system is one of the best in the world, but I must admit we lack maintenance," he said.