DenCity | Devpost

Inspiration

Have you ever driven 30 minutes to the beach only to find it completely packed? Or maybe you’re in a quiet city and just want to know where the nightlife and energy are tonight. Whether you're trying to find an empty gym, a quiet park, or chasing a bustling crowd, navigating urban density is a guessing game. We built DenCity to take the guesswork out of finding your ideal vibe, seamlessly and safely.

What it does

DenCity is a real-time "vibe check" for your city. By crowdsourcing Bluetooth device signals, we generate a live heat map showing exactly how dense an area is. It tells you if a train is packed, if there are cars on a street (for parking), or which parts of a theme park are currently a ghost town.

More importantly, our true innovation is security. DenCity provides this data without mass surveillance or tracking.

How we built it

We crowdsource data by scanning for nearby Bluetooth devices. Crucially, we only look at the front part of the MAC addresses (the OUI) to classify the type of device (e.g., a car system vs. a mobile phone) so we cannot identify anyone.

We encrypt this data and send it to our Supabase database. To guarantee absolute privacy, no Personally Identifiable Information (PII) is ever extracted, and the data is completely ephemeral—it lives in the database for only a few minutes to update the live heat map before being wiped clean. The frontend is built with React, communicating with a Node.js/Express backend.

Challenges we ran into

One of our biggest hurdles was figuring out how to listen to Bluetooth connections. Also, collecting real data and displaying it on a map. Another one was figuring out how to distinguish between cars and pedestrians. Relying on Bluetooth MAC address prefixes to identify vehicular tech isn't 100% perfect yet, and refining that classification logic took significant effort. We also had to build a robust pipeline to handle the real-time, highly ephemeral nature of the data while ensuring smooth frontend-backend communication.

Accomplishments that we're proud of

We are incredibly proud of our privacy-first architecture. We proved that it's possible to build a crowdsourced density map without compromising user data or resorting to creepy tracking (honestly, Google Maps knows way more about you than DenCity does!). Successfully visualizing this live data on a user-friendly heat map using Supabase was a massive win for the team.

What we learned

We learned a massive amount about privacy-by-design, managing ephemeral databases, and how to glean useful insights from raw Bluetooth signals without crossing the line into surveillance. We also leveled up our full-stack development and real-time data handling skills.

What's next for DenCity

To build our initial user base, we plan to launch hyper-locally—targeting a single college campus or a specific neighborhood to build strong network density. From there, we want to tune heatmaps to more precisely determine busyness in various areas.