Researchers have been working on ways to “see” people without using cameras or expensive LiDAR hardware for years. In 2013, a team of researchers at MIT found a way to use cell phone signals to see through walls. In 2018, another MIT team used Wi-Fi to detect people in another room and translate their movements into walking stick figures. Now, researchers at Carnegie Mellon University and the University of Waterloo are advancing our ability to see through walls using Wi-Fi.

How it's possible to see through walls

The researchers at Carnegie Mellon University have developed a new method for detecting three-dimensional shapes and movements of human bodies in a room, using only Wi-Fi routers. The team used DensePose, a system for mapping all of the pixels on the surface of a human body in a photo, which was developed by London-based researchers and Facebook’s AI team. Essentially it is a way to capture a set of coordinates for each joint like an arm, a head, a torso, etc., which is known as a key point that can describe a person's pose. They then created a deep neural network that maps Wi-Fi signals’ phase and amplitude sent and received by routers to coordinates on human bodies.

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The technology works by sending a low-powered Wi-Fi signal through a wall, which reverberates around the room. It detects all the objects in the room, cancels out the static objects, and when the signal bounces back, uses the reflection of moving objects to generate a radar-like image. It can work through standard drywall, wooden fences, and even concrete walls, though the range and accuracy depend on the type of wall.

Technology and the issue of privacy rights

The Carnegie Mellon researchers believe that Wi-Fi signals “can serve as a ubiquitous substitute” for normal RGB cameras when it comes to “sensing” people in a room. Using Wi-Fi, they wrote, overcomes obstacles like poor lighting and occlusion that regular camera lenses face. They also argue that this technology offers an improvement in privacy rights as it does not rely on cameras, and the required equipment can be bought at a reasonable price. Most households in developed countries already have Wi-Fi at home, and this technology may be used to monitor the well-being of older people or identify suspicious behaviors at home.

Researchers at the University of Waterloo have developed a drone-powered device called Wi-Peep that can see through walls using Wi-Fi networks. The device can fly close to a building and utilize the Wi-Fi network of the inhabitants to identify and locate any Wi-Fi-enabled devices within the building. Even if a network is password protected, smart devices will automatically respond to contact attempts from any device within range. The Wi-Peep sends several messages to a device as it flies and then measures the response time on each, enabling it to identify the device's location within a meter. 

Why Wi-Peep is noteworthy

What makes the Wi-Peep particularly noteworthy is its accessibility and ease of transportation. The team built the device using a store-bought drone and $20 of easily purchased hardware. This means that anyone with the right expertise could easily create a similar device.

The potential uses for this technology are vast, from law enforcement storming a building to firefighters looking for people in a burning building to search and rescue operations. However, the privacy implications are also significant, and it is important to consider the potential consequences if the technology were to be used for more sinister purposes.