Photos: Low-cost tech aids basic needs

The Solar Aid, invented in 1992 in Botswana, is a solar-powered hearing aid that costs less than $40 (£20). Batteries that keep it working at night need to be changed almost monthly. The beige hearing aid is shown here plugged into a solar charger. Manufacturer Godisa, a nonprofit, is the only maker of hearing aids in Africa and has staff members with hearing impairments.

More than 400 million people in the developing world are believed to be hearing impaired, yet most have no access to hearing aids.

Credit: Godisa Technologies Trust

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