Cell towers in Sannois (Val-d'Oise)

1 bridge or viaduct and 12 buildings and 3 pylons carry the commune's antennas.

Masts stand at 2 Rue du Bas des Conches, 2 Avenue du Marechal de Lattre de Tassigny, Butte de Montrouillet, Les Tartres, La Commanderie and 58 rue Marechal Joffre.

Over the past 12 months ANFR recorded 8 new systems here. ANFR has approved 2 new sites that are not live yet, plus additions on 3 existing masts. New: Bouygues Telecom (3G, 4G and 5G, including 5G at 3.5 GHz) at 1 Rue Saint Denis and Free Mobile (4G and 5G, including 5G at 3.5 GHz) at Le Pre Brochet. 11 Bouygues Telecom 5G transmitters are listed as technically operational — installed, but not yet declared commercially in service.

Most antennas sit on rooftops (12 of 16), so heights stay modest; the tallest support is 53 m at Butte de Montrouillet.

Systems from 1995 are still on the register. Bouygues Telecom switched on the first 5G here in November 2020; Free Mobile followed in December 2020, SFR followed in April 2021. 2015 was the busiest year, with 36 new systems, most of them 4G.

On 3.5 GHz, the fastest 5G band: Free Mobile on all 7 masts, Bouygues Telecom on 5 of its 6 masts, Orange on 5 of its 6 masts and SFR on 5 of its 6 masts.

2.1 km to the south, neighbouring Argenteuil has 60 masts, more than here.

Only one mast carries all four networks; 4 supports carry only Free Mobile.

At 5 km² with 26,924 residents, the commune is dense enough that most antennas sit on rooftops rather than pylons. It is part of the CA Val Parisis intercommunal grouping.

Figures above cover installations declared to ANFR as in service or technically operational, as of October 2026; approved projects are not counted.