The tsunami early warning system, parts of which were installed far off the coast of Sumatra, was down when the Indonesian island was struck by a magnitude 7.8 earthquake on Wednesday night.
The 22 deep-sea sensors, spread around the country, were "not active" because of a lack of funds to run and maintain them, said Indonesia's national disaster management agency (BNPB).
However, spokesman Djoko Hartoyo for the Coordinating Ministry of Maritime Affairs told the Wall Street Journal that the malfunction was due to "vandalism", blaming fishermen for tampering with the buoys by removing the antennae. This, he added, prevented critical data from being transmitted to the tsunami warning centre in Jakarta.
"The sensors would give us confidence about how we should handle (the situation) if a tsunami were to happen," Dr Sutopo Purwo Nugroho, who heads BNPB's data and information section, revealed at a press conference yesterday.
The sensors would, among other things, confirm a tsunami occurrence, and provide accurate data on how high and fast the waves were moving, as well as where they were heading.
There were five other buoys with working sensors operating that night, but they were all foreign-owned, said Dr Sutopo.
A ship with military and search and rescue personnel was sent yesterday to check on remote coastal communities, including those on the Mentawai Islands - the closest land mass to the epicentre.
Sumatra was unscathed yesterday despite being hit by 11 aftershocks. No serious damage and no casualties were reported in areas in the path of the quake, which was detected about 808km from Padang in West Sumatra, said Dr Sutopo.
This was because the tremors were caused by the Indo-Australian and Eurasian tectonic plates grinding past instead of slipping under each other, which would have been catastrophic, he noted.
The 11 aftershocks measured between 4.7 and 5.5 on the Richter scale, but residents in the Mentawai Islands, located just off Padang, still ran to the hills for safety.
There were also scenes of panic in the provincial capital - hundreds of residents fled to high ground on motorcycles as tsunami sirens were sounded. Patients were also evacuated from the local hospital.
Mild tremors from the quake were felt for a few seconds in Singapore, and as far north as Shah Alam, Subang and Klang in Malaysia.
The authorities issued a tsunami warning soon after the latest incident, prompting fears of a repeat of the magnitude 7.5 earthquake and ensuing 4m-high waves that ravaged Mentawai in 2010 and claimed at least 461 lives.
Wednesday's quake did trigger a tsunami that reached the Padang coastline - but BNPB recorded it at a mere 5cm in height, said Dr Sutopo. "It was not destructive, and did not damage any infrastructure or cause deaths."