Mobile data in San Francisco

A very good network on very awkward ground

San Francisco has the most demanding mobile users in the country and the carriers build accordingly. Downtown, Union Square, Fisherman's Wharf, the Mission, the Castro and SoMa are all strongly covered.

What the spending cannot fix is the shape of the place. Steep hills, narrow canyons and a city cut into ridges give San Francisco more dead spots than most comparably sized American cities. Twin Peaks and Glen Canyon both have patches with nothing, and so do parts of the Marin Headlands across the bridge. These are short and you walk out of them, but they are more frequent than the city's reputation suggests.

The Golden Gate Bridge itself has signal along the walkway. Fort Point, tucked underneath the southern end, has gaps — which is worth knowing because it is the one spot on that walk where people stop for a while.

Getting around here runs on apps

Muni and BART are both usable without a phone in theory and awkward without one in practice. Clipper, the regional fare card, is managed through its app. Google Maps routes San Francisco transit accurately but needs a live connection to reflect real-time changes, and Muni's schedules are irregular enough that the real-time part is the point. Ride-hailing fills in for the hills that Muni serves badly, which is most of them.

On BART, the above-ground sections have decent signal. We do not hold anything on the underground stretches, including the Transbay Tube, so plan on the assumption that a tunnel is a tunnel: load your route before you go down the escalator.

Alcatraz, and the road south

Alcatraz has WiFi provided by the National Park Service around the main visitor areas, and normal carrier signal works on the ferry and at the main dock. It is not the connectivity problem people expect an island prison to be.

The drive is the real one. Highway 1 south through Big Sur has long stretches with no signal at all — this is the single biggest coverage gap anyone leaving San Francisco is likely to hit, and it lasts a good deal longer than a canyon in the city. North into wine country, the main highways through Napa and Sonoma are fine; the smaller vineyard roads are patchier. Download offline maps for both drives before you set off.

What to buy

Prices marked verified were read from the provider's own site on 13 August 2026; the rest are indicative. Airalo sells the United States as two named tiers, Change and Change+, at every size — the Change prices are shown, and we cannot tell you what the dearer one includes.

That row used to name eSIM Go at $17, and then eSIMCard. eSIM Go sells wholesale to resellers and publishes no consumer price — checked on esim-go.com on 18 August 2026, where there is no basket, no checkout and no per-country page — so its rows cannot be bought or ever verified. See our eSIM Go page. eSIMCard is a working storefront, but its prices have been withdrawn too: we read its own pages on 18 August 2026 and the figures we held were not the ones it charges. See our eSIMCard page.

Since you will be dropping in and out of coverage on the hills, the sensible habit here is to let maps cache your area rather than re-fetch it. That saves more data than choosing between providers does.

None of these providers publishes which American network its plans roam onto. That matters more in San Francisco than in most cities, because the dead spots are network-specific in principle — but since nobody discloses the network, you cannot buy your way around them and the only real defence is offline maps. The full country comparison, including the 50GB tier that works out cheapest per gigabyte, is on our United States hub.

Buying a physical SIM

No ID is required and activation is instant, so a prepaid SIM is an ordinary retail purchase. A US airport counter runs around $20; stores in the city are cheaper. The case for one is a US number rather than better coverage — a restaurant confirming a table, or a driver who cannot find you on a hill.