LärmLupe Heilbronn · Green City Hackathon 2026
Make street noise
visible.
LärmLupe is a small, low-cost noise meter – the LärmBox – that measures traffic noise at Heilbronn windows and on walks, and puts it on an open, live map.
How it works
From a microphone
to an open map.
Measure
A sound-level sensor at a window or on a walk is read 20 times per second. Every second goes to the SD card, so nothing is lost.
Send
Once a minute the box sends LAeq, LAmax and LA90 to openSenseMap over WiFi. After a WiFi drop the backlog follows automatically.
See
The live map shows every box with its last three days. Walk recordings become an open dataset for the Green City Dashboard.
The device
Five parts,
one box.
The microphone sits outside the enclosure behind foam. The static box hangs outside the window, the mobile one is carried at 1.2–1.5 m on walks, together with the phone's GPS track.
Inside the LärmBox
Scroll to take it apart.
Five printed parts, six bought ones
Printed without supports, closed with M3 screws, open source down to the last millimetre.
- Main box
- Lid
- OLED display
- senseBox MCU
- Cable gland
- USB-C power
- Pod back
- Sound level meter
- Microphone pod
- Foam
- Rain hood
Open data, CC BY 4.0
Minute values are public on openSenseMap. Walk recordings become a GeoJSON dataset per place and time of day that anyone can reuse.
Dataset filesLevels only, no audio
The box never records sound – it only stores decibel values. No home addresses are used as places, and GPS tracks stay on our server.
Citizen measurement
Low-cost sensors, calibrated side by side. A way to see where and when it gets loud – not an official noise survey.
How loud is it right now?
Every LärmBox, live from openSenseMap, refreshed every minute.