Why does my phone say "Sign in to network" on public WiFi?

That message means the network is running a captive portal. Your phone tested the connection in the background and found that internet access is blocked until you log in, so it surfaces a notification prompting you to complete the sign-in page.

What is the difference between a captive portal and a splash page?

The captive portal is the underlying system that intercepts network traffic and controls access. The splash page is the branded screen it displays, with the venue's logo, login form, and any offers. One is the mechanism, the other is the interface guests actually see.

Is captive WiFi safe to use?

A captive portal itself is not a security risk, but any open public network carries the usual risks of public WiFi. Attackers can occasionally set up a fake hotspot with a matching name (an "evil twin") to intercept traffic before you reach the real login page, so using a VPN and sticking to HTTPS sites is still good practice.

Why does captive WiFi keep logging me out?

Most captive portals authorize a device by its MAC address, and address randomization can occasionally cause repeated logouts. But iOS and many Android versions keep a private address fixed per network rather than changing it on every reconnect, so session expiry, a VPN, or a browser blocking cookies is usually the more likely cause.

Does captive WiFi slow down my connection?

The portal itself only adds a few seconds during the initial login. If browsing feels slow afterward, that is almost always a bandwidth limit the network operator has set deliberately, not a side effect of the captive portal.

What Does Captive WiFi Mean? A Plain-English Explanation

Q: What does captive WiFi mean?

Captive WiFi is a public or guest network that holds a connecting device in a restricted state until it passes through a login page called a captive portal. The device gets an IP address but cannot reach the open internet until it completes whatever the portal asks for, such as an email address, a click-through agreement, or a voucher code.

Captive WiFi is a public or guest network that holds your device in a restricted state until you interact with a login page. You get an IP address the moment you join, but the network blocks everything else until you complete a step on that page, such as entering an email address, accepting terms, tapping a button, or entering a voucher code.

You've almost certainly used one without knowing the name for it: the WiFi at a coffee shop, hotel, airport, or gym that redirects you to a branded screen before letting you browse. That redirect, and the system behind it, is what "captive" refers to.

The "captive" part refers to your device, not you

When you connect to a network running a captive portal, your device is technically online (it has a local IP address) but "captured" by the network's router, which intercepts outbound traffic and redirects it to a single destination: the login page. Your phone or laptop typically detects this automatically and either opens a small browser window or shows a notification such as "Sign in to network."

Once you complete the login step, the router authorizes your device (usually by its MAC address) and clears the restriction. From that point on, you have normal internet access for the length of the session.

How the redirect actually works

Join the network. Your device connects and receives a local IP address from the router.
Traffic gets intercepted. The router blocks everything except a connection to the portal server. Your device's own background connectivity checks (Apple's captive.apple.com or Android's connectivitycheck.gstatic.com) get intercepted too, which is exactly how your phone knows to show the login prompt.
You complete the portal. Whatever the operator has configured, such as email capture, a single click, or a voucher code, runs on that page.
The router authorizes your device. Full internet access opens up, typically for a set session length.

Key point: http:// is the clean redirect path. A portal can rewrite a plain HTTP request and send you straight to the login page. It generally can't do the same to an HTTPS request without your browser throwing a certificate warning, so HTTPS sites more often just hang or time out instead of redirecting. That's why trying a plain http:// address is the reliable way to trigger the login page.

Captive WiFi vs. a regular WiFi network

A regular network, such as your home WiFi, has no intermediate step. You enter the password once and every device on it can reach the internet straight away. Captive WiFi adds a gate between joining the network and reaching the internet. The wireless signal itself is identical; it's the access policy sitting in front of it that's different.

This is why captive portals show up almost exclusively on public or guest networks rather than private ones. A venue offering open WiFi to strangers usually wants some form of consent, identification, or accountability before granting access, whether for legal reasons, network security, or simply to know who's using the connection.

Captive portal vs. splash page: they're not the same thing

These two terms get used interchangeably, but they describe different layers. The captive portal is the underlying system doing the redirecting, the traffic interception, and the device authorization. The splash page is the branded screen you actually see: the logo, the login form, and any promotional banner or offer.

Two venues can run the exact same captive portal software and show completely different splash pages: one a bare "Accept and Connect" button, another a full form asking for a name, email, and marketing consent. The portal mechanics are identical either way. Only the front-end design and the data being requested change.

When captive WiFi isn't working

The login page never appears

Open any plain http:// address in your browser rather than an HTTPS one. Try http://neverssl.com, which is built for exactly this. The portal is listening for unencrypted traffic and will intercept it and load the login page.

The page loads but won't submit

A VPN, an ad blocker, or a browser blocking third-party cookies can interfere with the authorization step. Try disabling them temporarily, or use a different browser.

You keep getting logged out

MAC address randomization can be a factor, but it's less common than people assume: iOS keeps a private address fixed per network (or rotates it roughly every two weeks) rather than changing it on every reconnect, and many Android versions do the same. If you're being logged out repeatedly, session expiry, a VPN, or a browser blocking cookies is usually the more likely cause. Check those first before touching your device's privacy settings.

FAQ

What does captive WiFi mean?: A public or guest network that requires you to complete a login step, such as email, terms acceptance, or a voucher code, before granting full internet access.
Why does my phone say "Sign in to network"?: Your device detected that the network is blocking internet access until you complete a captive portal login, and it's prompting you to do so.
Is captive WiFi safe to use?: The portal itself isn't a risk, but public WiFi in general carries the usual risks, including "evil twin" networks impersonating a legitimate one. A VPN and HTTPS-only browsing are still worth using.
Why does captive WiFi keep logging me out?: MAC address randomization can occasionally be the cause, but iOS and many Android versions keep a private address fixed per network rather than changing it each time. Session expiry, a VPN, or a browser blocking cookies is usually the more likely explanation.
Does captive WiFi slow down my connection?: The portal itself only adds a few seconds during login. If browsing feels slow afterward, that's almost always a bandwidth limit the operator has set deliberately, not the captive portal itself.

If you're the one setting up a captive portal for a venue rather than trying to connect to one, say for a restaurant, hotel, or retail location, the mechanics above are exactly what you're configuring, just from the other side. Our guide to what a captive portal is for hospitality operators covers how to set one up, capture guest data compliantly, and turn it into a marketing channel rather than just a login gate.