Research Prototype · 2025
Turning Old Smartphones into
Battery-Free Environmental Sensors
We explore how a retired smartphone can continuously monitor its surroundings and send useful data — using wind and solar energy rather than its internal battery.
The Problem
Environmental monitoring often requires dense sensor networks that are expensive, power-hungry, and difficult to maintain. In many regions, replacing or charging batteries is the biggest barrier to long-term deployment.
Meanwhile, millions of smartphones are discarded every year. Most of them still have functional sensors — microphones, cameras, accelerometers — but their batteries are degraded or dead.
Key Challenges
- How can we operate sensing hardware without a traditional battery?
- How much useful data can a “dead” phone still provide?
- Can we build a stable, low-maintenance system from e-waste?
Our Idea
We treat an old smartphone as a modular sensing unit powered by external energy harvesting modules instead of its original battery.
The device captures raw environmental signals — such as light, and motion — and forwards compact summaries to a lightweight server or local hub.
Our Approach
1. Upcycle
Use retired smartphones as sensor nodes instead of buying new hardware.
2. Harvest
Replace the phone battery with solar / RF / supercapacitor-based power input.
3. Sense
Run lightweight sensing tasks: basic image capture, motion patterns.
4. Report
Send aggregated metrics or event alerts to a monitoring dashboard.
System Workflow
Below is the high-level pipeline that connects the physical environment to human-readable insights — using only an old phone and minimal external hardware.
Passive Sensing
Phone sensors capture raw data (audio snippets, low-res frames, IMU samples).
On-Device Processing
Lightweight models or thresholds detect events (e.g., bird calls, noise spikes).
Data Uplink
Compressed summaries or labels are transmitted when energy is available.
Dashboard & Research
Researchers visualize time series, event frequency, and environmental trends.
Early Results
In our initial experiments, a single recycled smartphone mounted outdoors and powered by a small solar panel was able to collect data continuously over multiple weeks, without any manual charging.
We validate that even in low-power conditions, the device can:
- Capture acoustic patterns (e.g., traffic noise, bird activity).
- Detect motion or vibration events via IMU sensors.
- Upload summarized data whenever sufficient energy is available.
Sponsor
We thank the National Science Foundation (NSF) for their generous support, which makes our research possible.
Our Donors
Special thanks to our donor: Mrs. Linda Bowman.
Research Team
This project is part of an ongoing effort to reduce e-waste and build sustainable sensing systems.
Gilmore Troy
Associate Professor University of Nebraska–Lincoln
Andrew Richardson
Regents' Professor, ECOSS/SICCS Northen Arizona University
About Wireless and Sensor Systems Lab
WSSL's broad research interests are in the areas of AI-powered mobile/wearable computing and sustainable computing. Our research agenda focuses on Sustainable Autonomous Things (SATs) for realizing the vision of:
- the Internet of Sustainable Medical Things
- the Internet of Sustainable Living Things
- and the Internet of Sustainable Flying Things
Our work is interdisciplinary in nature, combining innovations in sensor and sensing system development, algorithms, data analytics, signal processing, hardware, and firmware optimization to invent:
- A new class of medical devices that can continuously and unobtrusively collect novel and important health data in non-clinical settings.
- A new class of living sensors that can live with plants and animals.
- A new class of unmanned aerial vehicles requiring extremely low maintenance.
- We are also interested in sustainable quantum computing. Together with Berkeley Lab, we have made exciting progress.