Sharing a device: what a VPN does and does not isolate

People reach for a VPN on a shared device expecting a privacy boundary between the people using it. It does not provide one, and the reason is structural: a tunnel is a property of the network connection, and everyone on the device shares the network connection.

What is shared regardless

Browser history, unless each person has a separate browser profile.

Saved passwords and sessions, unless the operating system accounts are separate.

Downloaded files.

Cookies, so a site one person logged into recognises the next.

The tunnel itself, which is either on for everyone or off for everyone.

A VPN changes none of that. It changes what the network operator and the destination sites see, identically, for everyone.

What actually separates people

Separate operating system accounts. The real boundary. Windows, macOS and Linux all support them properly, with separate home directories, separate browser data and separate saved credentials.

Separate browser profiles, if separate accounts are impractical. Weaker, because anyone can switch profiles, and much better than nothing.

Android's multi-user support on tablets, which gives each user their own apps and data. Phones generally do not enable it.

Screen Time or Family Link for parental controls, which are a different thing again — they restrict rather than separate.

Where the VPN interacts with this

Two ways worth knowing.

A tunnel applies system-wide, across all accounts. One person turning it on turns it on for everyone currently using the device, including a second user signed in simultaneously on a desktop operating system.

Per-app or split tunnelling is also shared. A rule excluding an application excludes it whoever runs it.

So on a family computer, the VPN is a household-level setting rather than a personal one, and it should be configured as such: on by default, with the few exclusions everyone needs.

The case where it does help

A shared device on an untrusted network — a laptop taken to a café, a tablet used in a hotel — benefits from a tunnel for exactly the reason any device does. The network operator does not learn what the household did.

That is a genuine benefit and it is about the network rather than about the people sharing the device.

What to do instead

If the goal is that one person's activity is not visible to another:

1. Separate operating system accounts, with passwords.
2. Separate browser profiles within each account if needed.
3. Sign out of shared accounts rather than relying on private windows.
4. Full-disk encryption, so a lost device does not expose everything.

None of those is a VPN, and all of them are more effective at the thing being asked for.

Setting it up sensibly on a shared machine

Install the client for all users where the platform distinguishes, turn on auto-connect and a kill switch, and leave it running. On Windows that means the service starts at boot rather than at login, so the tunnel is up before anyone signs in.

Then treat it as infrastructure — something the household has, like the router — rather than as a personal privacy tool that each person manages.

The honest boundary

A VPN protects a device's traffic from the network. It has no concept of who is typing. Anyone who wants privacy from the people they live with needs account separation, and the privacy policy question — what the provider records — is about the household's traffic as a whole, not about any individual in it.

Household filtering is a separate tool again

Parents frequently want two things at once: privacy from the network operator, and control over what children can reach. A VPN does the first and actively interferes with the second, because DNS-level filtering configured on the router is bypassed by a tunnel with its own resolver.

If both matter, the workable arrangements are filtering applied inside the same tunnel — some providers offer a filtering resolver option — or per-device policies using the platform's own parental controls rather than the network.

Configuring filtering on the router and a tunnel on the devices produces a setup where the filtering silently does nothing, which is the worst outcome because it looks like it is working.

Guests

A household VPN covers guests joining the Wi-Fi if the tunnel is on the router, and does not if it is on individual devices.

That is worth thinking about once. Routing a visitor's traffic through a provider they did not choose is a defensible default and it is a choice you are making on their behalf, and a guest network without the tunnel is the cleaner arrangement in most homes.

Devices that cannot have accounts

Televisions, speakers and consoles have no meaningful user separation, and everything on them is shared by whoever is in the room. A tunnel on those devices protects the household's traffic from the network and separates nothing, which is the same conclusion as everywhere else in this article — just with no alternative available.