A shrieking, flashing alarm plugged into a household power point could be just the thing for Northlanders in danger of sleeping through a tsunami siren.

The lunchbox sized alarms are the result of Northland Civil Defence Emergency Management (CDEM) Group wanting to cast the net wider to warn people in evacuation zones of a pending tsunami.

As well as an ear-piercing noise, the boxes emit a bright blue flashing light which deaf people would see, should the alarm go off while they were awake or in the same room.

"We're introducing them for those who, for whatever reason, may be unable to hear local outdoor tsunami sirens," said Victoria Harwood, from Northland CDEM.

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About the size of a small lunchbox, they have been developed in conjunction with Northpower which assembles them in Whangarei, and are unique to Northland at this stage.

Ngunguru resident Nadie Tillman was among the first to buy one last week when Northland CDEM started selling them.

The small device would provide extra peace of mind, she said.

Tillman's home is beside the Ngunguru estuary. She was in Whangarei Hospital and unable to sleep on the night of the Kaikoura earthquake.

''There was potentially going to be tsunami, and I was calling my family at home to warn them to be alert. No-one answered the phone, they slept through it.

''It was a terrifying feeling, trying to warn them and being unable to.''

Tillman realised that if they slept through that, there was a strong chance they would sleep through the Ngunguru tsunami alarm.

''We do hear them when they're tested but that's always during the day.''

The plug-in sirens are available to consumers on the Northpower or Top Energy power supply networks and are being sold for their cost price of $155.25.

Although intended for property owners, residents and businesses Northland-wide, they can only be purchased in person from the Northland Regional Council, Water St, Whangarei.

Purchasers must have a brief face-to-face introduction to their new indoor siren's use before taking it away.

While CDEM has stated it had hearing impaired consumers in mind when the unique-to-Northland sirens were developed, a member of that community said they might be of little use to the profoundly deaf.

However, tsunami warnings were also broadcast on the radio, which was even less help, she said.

Safety and help items for deaf people usually had to be approved, endorsed and sometimes funded by the Ministry of Health.

Special fire alarms for the deaf were assessed and installed through the fire service, Harwood said.

''We already have access to all kinds of flashing and vibrating alarms and lights.''

But initiatives for public safety were always welcome, she said.