Each year, over a billion smartphones are manufactured, yet most are replaced within two to three years, even if they’re still working. That’s usually because their software becomes outdated, the battery degrades, their performance slows down, or users are tempted to buy the latest models. 

As soon as the new phone arrives, the old phone is either collecting dust in the drawer or, worse, it becomes a part of the ever-growing e-waste problem. One 2021 estimate found that electronics waste totaled 57.4 million tons for that year, which is greater than the mass of the Great Wall of China. However, what if these old phones could be repurposed into something very useful? That’s exactly what a team of researchers in Estonia set out to do.

In their new study, they’ve shown that aging smartphones, even the ancient variety over a decade old, can be turned into miniature data centers. These repurposed devices can handle tasks like image recognition, environmental monitoring, and even help optimize city transport systems. And the best part is that each such unit would cost just eight euros (~$9.30) to build. 

“Innovation often begins not with something new, but with a new way of thinking about the old, re-imagining its role in shaping the future,” Huber Flores, one of the study authors and an associate professor of pervasive computing at the University of Tartu in Estonia, said.

Old Smartphones, Modern Data Centers

The study authors found a way to transform outdated smartphones into efficient computing units. They began by tackling a few key challenges. For instance, old phones often have degraded batteries and security vulnerabilities. 

The team removed the batteries entirely, eliminating the risk of chemical leaks, and replaced them with safe external power sources. This step alone made the phones more environmentally friendly and stable for long-term use.

Next, the researchers connected four old Google Nexus smartphones into a cluster, using one phone as the master and the others as workers. The master device performed tasks like analyzing camera footage or reading data collected by its sensors, and distributed the work to the other phones. 

All these devices were fitted into a custom-made 3D-printed casing and loaded with Postmarket OS, a lightweight, open-source Linux-based system that replaced the phones’ original operating systems. This software switch allowed the team to control the phones more freely and securely.

In one experiment, they placed the phone-based micro data center in a waterproof bubble and dropped it 25 meters underwater near the Portuguese island of Madeira. Connected to a high-resolution camera, the system successfully identified and counted marine species, a task that would normally require a scuba diver and hours of manual video analysis. 

In another scenario, the researchers showed that such micro data centers could be placed at bus stops to collect real-time passenger data, which can help cities optimize their public transport systems. These experiments demonstrated that old smartphones, often tossed aside as junk, can be put to some great use.

“These phones, you can just get them from the trash. All you have to do is buy a module to regulate the voltage that you put into the phone from another source. Then you install the open-source system to control the hardware and make the smartphones work together, and you have a tiny data center that can be useful for many applications,” Flores said.

A Green Innovation With Major Benefits

The potential impact of this work could be huge. The world discards over five billion phones every year, many of which end up in landfills, leaking toxic substances like lead and mercury. Recycling methods currently recover only a fraction of the valuable materials inside, while the rest is lost or burned. 

By turning old smartphones into micro data centers, the researchers offer a new, sustainable path, one that extends the useful life of devices while reducing both e-waste and the need for new and costly applications for tasks like marine life tracking, water and air quality monitoring, forest surveillance, pollution mapping, and server hosting.

For instance, today, engineers and researchers often rely on single-board computers like the Raspberry Pi to build DIY servers, IoT devices, or lightweight data processing units. However, these boards offer limited computing power and typically cost over €50 ($58) each. 

In contrast, a repurposed smartphone that is equipped with more powerful processors and faster memory can outperform the single-board devices at a fraction of the cost, requiring just €8 ($9.30) to convert into a functional micro data center. 

“Sustainability is not just about preserving the future. It’s about reimagining the present, where yesterday’s devices become tomorrow’s opportunities,” Ulrich Norbisrath, one of the study authors, said.

However, there are some hurdles to adopting this approach on a large scale. For instance, unlike the modular Nexus series phones used in this study (easier to open and modify), many newer models are sealed and harder to hack, with proprietary software and designs that discourage reuse. 

The study authors hope that their success will push governments and regulators to introduce right-to-repair policies and encourage manufacturers to make devices more customizable, repairable, and reuse-friendly. 

The study is published in the journal IEEE Pervasive Computing.