Peter Holley Watching Fernando Albertorio stroll down a crowded footpath into downtown Washington during a recent lunch hour, casually sidestepping pedestrians running errands and crowding around food trucks, you'd have no idea he is legally blind.

Albertorio easily blends into the flow of human traffic swirling around him, which is even more remarkable considering that he is doing so largely without the use of his limited vision.

His secret: a wrist band called Sunu that emits a high-frequency sound wave that bounces off objects as far as 4.2m in front of him before registering as a gentle, pulsing vibration on his arm.

The closer the object is - whether it's a wall, rubbish can or person - the more frequent the pulses become, allowing Albertorio to create a mental map of the world around him using echolocation. He compares the device to sonar being used in vehicles to sense nearby objects and avoid crashes.

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Albertorio, who grew up in Puerto Rico, is part of a team of entrepreneurs from Mexico who built Sunu from scratch and are hoping their invention changes the way visually impaired people get around.

"One of my friends calls the device his 'sixth sense'," Albertorio said, noting that people with vision loss are sometimes afraid of going outside. "It enhances my awareness of my personal space and keeps me safe when I'm out in my neighbourhood."

For the visually impaired, smartphone apps can help them hail a ride, link to real-time maps and get to the nearest convenience stores. But there is no app for avoiding a tree branch obstructing a footpath after a storm or walking through a rush-hour crowd, not to mention finding an office in an unfamiliar building or the closest restaurant in a new neighbourhood.

"This is a way of getting people outside and doing things while being discreet," Albertorio added.

The device's settings, including range and sensitivity, can be customised using the company's app.

The visually impaired still rely largely on Seeing Eye dogs and the white cane - a tool that is nearly 100 years old and doesn't protect users above their knees.

The Sunu band isn't the first device to harness the power of echolocation. Inventors have created vibrating clothing that uses echolocation and a vibrating clip that uses ultrasound to help visually impaired people avoid obstacles above their lower body.

The challenge for engineers, Albertorio said, is creating technology that isn't obtrusive, distracting the user from the sensations and sounds visually impaired people rely upon. A vibrating cane might help a user detect large obstacles ahead of them, for example, but it can also numb the delicate sensations that allow someone's fingertips to perceive subtle changes on the ground below, Albertorio said.

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Because of the variety of navigational challenges visually impaired people face, there is no single solution for getting around, experts say. Having access to a portfolio of complementary navigational tools is often ideal, says Dave Power, the president and chief executive of Perkins School for the Blind, the US' first school for the blind. "If you're walking down the sidewalk and you're anticipating a corner, it's hard to beat a guide dog that knows you and can help you travel long distances. But if you drop your wallet on the floor, you might prefer using Sunu over using a cane, which might be a clunkier solution for finding a small object."