Ten recent low-tech inventions that have changed the world

By the early 1990s, diarrheal diseases were killing some 5 million children under the age of five every year. That number is down to about 1.5 million, thanks to oral rehydration salts—a mixture of salt and sugar that can be dissolved in water and administered at home. Zinc is sometimes added to the mix to reduce the severity and duration of diarrhea. This simple innovation has perhaps saved more lives at lower cost than any other.

Irrigation accounts for the bulk of fresh-­water use in most countries—something like three quarters of the total. Drip irrigation uses half as much water as conventional irrigation and is half again as productive. But it’s expensive and usually requires electrical power. The GEAR lab at MIT has developed low-pressure solar-powered drip irrigation systems that can deliver the benefits at much lower cost.

Solar cells can provide cheap, decentralized electricity. But if you’re plugging them into conventional devices on a normal household grid, there’s a lot of overhead involved in converting the direct current they produce into alternating current and back again. A well-designed small DC network can save a substantial amount of energy by eliminating this need.

Deforestation is a major problem in much of the developing world, as is the harm to human health that comes from breathing in the particulate matter in smoke from woodstoves. Better-designed stoves like the Berkeley-Darfur stove use only half as much fuel to cook a comparable amount of food, and they cut the particulate emissions in half as well.

Hundreds of millions of people around the world lack access to safe water. Simple, cheap water filters use ash combined with silver nanoparticles to filter out impurities and pathogens; they have improved the lives of hundreds of thousands.

Hundreds of millions of people, usually women, have to walk every day to get enough water for their basic needs and transport it home in buckets. The Hippo roller is a heavy-duty plastic barrel that can be flipped on its side and rolled home, via an attached handle, over rough terrain.

Vaccines are crucial for public health. But in the developing world, distributing the vaccine to where it’s needed is only part of the problem. How do you administer it in a place where sterile needles might be scarce? One fix is a jet injector, a decades-old invention that can send a high-­pressure, directed stream of fluid through the skin.

Microscopes are crucial for diagnosing infectious disease. But in some ways they’re the worst possible device—heavy, expensive, and hard to maintain. Paper microscopes, also known as foldscopes, contain all the crucial parts within one foldable sheet of paper. They can be optimized for different diseases and cost less than a dollar.

Cell phones are common even in poor countries, but when a natural disaster strikes, the communications networks these devices rely upon can fail. Developed in Chile, SiE is a system that encodes text into high-frequency audio tones that can be distributed over broadcast radio waves and received on any smartphone without requiring any internet infrastructure. An app on the phone listens for these tones and transforms them into a text message.

Malaria kills 1,200 children a day. Quick diagnosis and treatment is crucial, but that typically requires a microscope and a reliable technician to analyze blood samples. A quicker, simpler system developed last year at the University of Southern California is portable and detects levels of hemozoin, a by-product created by the malaria parasite, which reveals how far the disease has progressed.