Observatoire des Ondes: An EMF Sensor Network Born From a 5G Debate
This overview was generated with AI from the public sources listed below and checked against them before publication. It has not had a complete human fact-check — treat it as a starting point and follow the sources.
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Nantes asked mobile operators to suspend their 5G rollout in late 2020 and put the question to a citizen debate, "5G à Nantes : parlons-en !", which drew 404 contributions including 139 proposals across nine workshops. One commitment that came out of it was a permanent measurement network: around 50 battery-powered sensors mounted mostly on lampposts near schools and crèches, each taking a six-minute broadband reading across 80 MHz to 6 GHz roughly every two hours and reporting over a low-power radio network. Every reading is published under the Licence Ouverte on the metropolitan open data portal — 1,204,385 of them from 68 sensor sites between 4 March 2020 and 10 August 2026. Nantes Métropole commissioned the observatory and the contractor Exem operates the sensors; a metropolitan digital-infrastructure charter signed with the operators in 2023, replacing a 2013 version, carries the transparency commitment.
what does this mean?
The strongest source is the operator's or the city's own reporting — an official report, dataset or press release. It grades who did the looking — not how well the project went. All four grades →📊 Impact
Across the 1,204,385 readings published to 10 August 2026 the mean broadband field strength is 0.91 V/m and the highest single reading is 5.51 V/m. The exposure limits set by decree 2002-775 run from 37 V/m at 700 MHz to 61 V/m above 2.1 GHz, and the dataset's own over-limit flag is zero on every one of those records. The sensors report a single broadband figure spanning 80 MHz–6 GHz, so this is an exposure indicator rather than the per-band regulatory compliance test.
🎓 Lesson
The network answers a political question and nothing else: no reading triggers any action. The restriction on antennas near schools was tied to a national health-agency (ANSES) report rather than to a sensor threshold, and 5G was switched on across the rest of the metropolis after the debate. The network is also thinner than the headline suggests — 68 sites appear across the series but only 55 reported in the 30 days to 10 August 2026, and the series opens in March 2020 with three sensors, reaching 50 only during 2021.
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📎 Cite this project
1001 Smart Cities (2026). “Observatoire des Ondes: An EMF Sensor Network Born From a 5G Debate” — Nantes, France. The Smart City Atlas. https://1001smartcities.org/projects/nantes-observatoire-ondes/ (last verified 2026-08-10). Data: CC BY 4.0.
The underlying data is free to reuse with attribution — see the open data page.