It started with a train.
At 9 Mile & Hilton in Ferndale, a freight train can hold the crossing for thirty seconds or twenty minutes, and from a few blocks away there's no telling which. Heimdall listens for the train and reports, in real time, whether the gates are down. That's the first sensor.
One station, many questions.
The instrument at the crossing is a station: a small computer with a microphone, and room for more senses. The train watch is one question it answers — the same station could count passing trains, track how loud the street gets at night, or take on a question we haven't thought of yet. A new question arrives as software, not new hardware, and only its answers leave the site. The sound stays where it was heard.
Run by the people closest to it.
The bet behind citizen science is that the people who live with a problem are the ones who should measure it. Every station writes its answers to a shared, open record — and as stations and questions accumulate, so does a public picture of the neighborhood that anyone can check, question, and build on. That's still ahead of us to prove, and it starts with this one crossing.