Air raid-style tsunami sirens have been ruled out for the 45,000 people living in Tauranga's low-lying coastal suburbs because the noise they make will become illegal in three years.

The Ministry of Civil Defence and Emergency Management policy proved a bitter pill to swallow for some city councillors because of the public popularity of sirens symbolised by the Blitz in World War II.

There was dismay that the Ministry's national standard for the noise of a civil defence warning system did not fit the distinctive wailing of mechanical sirens. It meant that even if the council included the sirens in its suite of tsunami warning measures, the noise would fail to comply on July 1, 2020.

"They will fold on it, they don't have the guts," a frustrated Papamoa councillor Steve Morris declared.

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The news about mechanical sirens was delivered by the council's emergency management and safety manager Paul Baunton to a special workshop yesterday to decide which warning options deserved further investigation.

After nearly two hours of explanations and debate, the workshop agreed that more work should be carried out on the options of electronic speaker sirens mounted on power poles and small in-home sirens.

Mr Baunton's preferred option was in-home sirens because they were more affordable at $25 to $35 per unit and did not have the audibility issues of old-style sirens in windy conditions and the risk they would fail to penetrate modern homes with double glazing.

The workshop consisting of six members of the Community and Culture Committee saw Cr Larry Baldock make a late but unsuccessful bid to put the issue in front of the full 11-member council.

"It needs to be a collective 11-member decision."

He said the council was dreaming if it thought it could get air raid sirens through the consenting process.

Yesterday's decision effectively turned back the clock more than six years on tsunami warning systems to when a former council opted for a suite of alerting mechanisms that excluded air raid-style sirens.

However, tests of a power pole-mounted speaker system proved unsatisfactory and, under public pressure generated by the 2011 Japan tsunami, the council agreed to reconsider traditional sirens.

In-home devices were assessed as 82 per cent effective, with the advantage that the radio signal activated alarm incorporated a message. Fixed mechanical sirens were 44 per cent effective and did not carry a message.

Councillor Bill Grainger said that no matter where you were and or what you were doing, you heard something from old-style sirens.

He was assured by Greg Holland of GMS Science that the 44 per cent figure was the experience from around the world when sirens were used in isolation.

Undaunted, Cr Grainger told Mr Holland: "You need to watch a few World War II programmes and see what they did then."

Mr Baunton said Tauranga needed a system that hit most people quickly. The Kaikoura earthquake showed that some people did not hear the alert because their cellphones were not in the bedroom.

He said there was no single silver bullet but a suite of things working together. The GeoNet monitoring and early warning system was set up after Kaikoura.

Mr Holland said a lot of work was currently taking place on shrinking the 60 to 75 minutes it took to assess a tsunami and issue an alert.

Further work on the favoured options would include funding and a possible one-off compulsory charge on householders for the device in areas of the city vulnerable to tsunami. The device would be replaced every 10 or 15 years.

Garry Towler of the Thames Coromandel District Council said air raid sirens were horrendous to maintain and when they pushed the button in the last tsunami alert, 10 per cent failed to go off. They needed another 40 sirens to be effective.

Advantages of air raid sirens include
- Met public expectations
- A night-time solution
- Publicly owned and maintained.

Disadvantages of air raid sirens include
- Expensive (more than $2.5 million for a network)
- High annual maintenance costs (more than $500,000)
- Limited reach