South Africans social entrepreneurs have come up with inventions aimed at curbing deadly fires and floods in the country's crowded informal settlements.

A turquoise detector no bigger than a pack of cigarettes is among the innovations being showcased at a technology exhibition in the capital Pretoria.

While a conventional fire detector is set off by smoke, Lumkani, meaning "be aware" in the Xhosa language, looks for another signal: heat.

"Shack environments tend to be fairly smokey because of a lack of electrification," Lumkani's co-designer, University of Cape Town engineering lecturer Samuel Ginsberg, said.

"Shack dwellers often use fire inside their shacks for cooking. So a normal smoke detector, which is what you would use in your home, is not effective -- it would false trigger far too often."

Lumkani's alarm is set off instead by a quick and unusual rise in temperature.

Fires spread quickly in the dense slums that ring many towns and cities in South Africa.

Packed close together, the shacks of wood planks and plastic sheeting are often razed to the ground within minutes.

A series of mid-summer fires in 2013, fuelled by gusty winds, tore through the Cape Town townships of Khayelitsha and Thembeni, leaving around 4,000 homeless in just two days.

Lumkani was not the only invention on display in Pretoria that aims to improve the lot of the poor.

A group of high-school students have created a platform of recycled crates and plastic bottles, which can be inserted under shacks to avoid flooding.

"The idea behind this is that if you build a shack on top of the crates, they will lift the shack out of the water during flooding," Ayanda Noma, director of Innovation and Technology at the University of South Africa, explained.

"What we are trying to do is prevent loss of life, loss of belongings and sometimes loss of livelihoods that accompanies flooding in informal settlements," said Noma.

Lack of housing in urban areas is one of the main challenges facing South Africa, where many of those who flock to cities in search of a better life wind up living in slums.

"As a small enterprise we cannot hope to take a billion people living in shacks and get them out of their shacks and into civilised dwellings that they deserve to live in," said Ginsberg.

"The best we can do is take the shack environment and make it a better place to live in."