Pulse

Inspiration

Crowd crushes rarely come out of nowhere. Before people get hurt, the crowd starts moving in waves: one person is pushed into the next, and the push travels through the crowd. Everyone in that crowd is already carrying a motion sensor in their pocket.

What it does

Pulse is an early warning system for crowd crushes that uses the phones already in the crowd. Phones open a web page (no app install) and stream their motion to a server. When neighbouring phones start swaying together in a wave that travels from person to person, the zone turns yellow, then red. Staff see it on a live dashboard map, Gemini writes a short briefing, ElevenLabs reads it out loud, and an Arduino sign flashes a warning. Phones in the danger zone get an arrow pointing to the less crowded way out.

Jumping or dancing together does not trigger it: everyone moving at the same moment is not a travelling wave. Math detects, AI only explains.

How I built it

Go server: one binary serves the phone page, the dashboard, WebSockets and APIs. It syncs each phone's clock, cross-correlates the motion of neighbouring phones to find travelling waves, and tracks crowd density.
TypeScript + Vite for the phone page and the dashboard.
Tiger Data stores readings and alerts for replay.
Gemini writes the staff briefing, ElevenLabs speaks it.
Arduino Uno R4 WiFi sign that shows the zone level.
A crowd simulator (Social Force Model) so the whole thing could be built and tested solo, without a real crowd.

Challenges

Phones are carried at any angle, so every reading has to be levelled using gravity before it can be compared.
Phone clocks disagree, so each phone gets an NTP-style clock sync.
Telling a dangerous push apart from dancing, walking, or someone just checking their phone.
Every external service has to fail soft: detection keeps running with no internet.

Privacy

No names, contacts, audio or photos. Just a random session ID, a position inside the venue, and motion numbers.

What's next

Build it into an event's official app so it keeps running when the screen is off.
Better positioning of phones in a real crowd.
Tuning thresholds with much larger crowds.