The unseen side of GPS: ‘Fine-grained’ data can expose far more than just location

GPS guides us to places or help us track our online orders. But the “fine-grained” data collected by it on Android smartphones can reveal far more than just the location, quietly exposing a person’s activity, environment or even layout of the room they are in, according to a study conducted by IIT-Delhi.

The study titled, “AndroCon: An Android Phone-based Sensor for Ambient, Human Activity and Layout Sensing using Fine-Grained GPS Information” has been published in ACM Transactions on Sensor Networks, a top journal in the field of privacy-aware sensing.

The researchers proposed AndroCon, the first system to demonstrate that the “fine-grained” Global Positioning System (GPS) data already accessible to Android apps with precise location permissions can act as a covert sensor.

Without using the camera, microphone, or motion sensors, AndroCon interprets nine low-level GPS parameters — such as the Doppler shift, signal power, and multipath interference — to infer whether someone is sitting, standing, lying down, inside a metro, on a flight, in a park, or in a crowded outdoor space.

They can also infer if the room is crowded or empty. To turn this noisy raw data into clear insights, they combined classical signal processing with modern machine learning.

“Across a year-long study spanning 40,000 sq km and a lot of different phones, AndroCon achieved up to 99 per cent accuracy in detecting surroundings and over 87 per cent accuracy in recognising human activities, even subtle ones like hand-waving near the phone,” said Smruti R Sarangi, professor, Computer Science and Engineering Department, IIT-Delhi.

The same framework can also sketch indoor floor maps — identifying rooms, staircases, and elevators — with a margin of error under 4m, using only GPS patterns and user trajectories.

While AndroCon opens exciting possibilities for context-aware, privacy-respecting smart services, it also exposes a critical security gap. Any Android app with precise location permissions could potentially infer sensitive contextual information without explicit user consent.

“This study reveals an unseen side of GPS. A powerful but silent channel that can sense the world around us. AndroCon turns the everyday smartphone into an unexpectedly precise scientific instrument and a reminder that even the most familiar technologies still hold hidden secrets that can be misused by malicious entities,” Sarangi added.