iPhone connects to some Wi-Fi networks automatically, here's the criteria it uses to prioritize Wi-Fi networks

You may have noticed that your iPhone, iPad and iPod touch attempt to auto-join known wireless networks. That said, have you ever wondered how exactly the mobile operating system determines which Wi-Fi network it should attempt to join automatically?

Why’s this important?

macOS simply attempts to auto-join the Wi-Fi network your computer has most recently connected to. iOS, on the other hand, handles Wi-Fi connections differently. That’s OK because you predominately use your iPhone, iPad or iPod touch on the go, where a bunch of nearby Wi-Fi networks are vying for its attention all the time.

A Settings app screenshot showing an iPhone 7 being connected to a password-protected wireless network

Secure Wi-Fi networks are password-protected and have a padlock icon by their names

Knowing how iOS decides which Wi-Fi network your iPhone or iPad will join automatically can go a long way toward optimizing your wireless performance by prioritizing your favorite networks over those you maybe joined once in the past, like a Wi-Fi in a random coffee shop.

How iOS decides which Wi-Fi to auto-join

When auto-joining networks, iOS tries to connect to networks in the following order:

  • Your most preferred network: This is the Wi-Fi network you most frequently use.
  • The private network you most recently joined: This requires no further explanation.
  • A private network: Private networks are also known as Virtual Private Networks, or VPNs. Your device may have connected to a private network if you used one of the popular VPN apps, like NordVPN. Aside from VPNs, private networks are also those you set up in homes and offices and the Personal Hotspot on your iOS device.
  • A public network: If you connected to a Wi-Fi network from a hotel, airport, coffee shop or other public locations, you joined a public network. Some other examples of public Wi-Fis include Hotspot 2.0, Passpoint, EAP-SIM or Wi-Fi connections that are provided by some cellular carriers and cable providers.

Read on to learn why you should care and what all of the above means in terms of daily use.

Real-world examples

Here’s one typical example.

Say your home Wi-Fi is the most preferred network on your iPad. Let’s pretend you’ve used the Personal Hotspot feature recently to share your iPhone’s cellular connection with the tablet over Wi-Fi. Also, imagine you take advantage of a VPN service occasionally on your Apple tablet to bypass regional restrictions for video-streaming apps.

EXPLAINER: How iOS 11’s redesigned Bluetooth and Wi-Fi toggles in Control Center work

If you’re outside your home Wi-Fi’s reception and you’re not using a VPN service, your iPad will attempt to connect to the Internet via Personal Hotspot on the phone. As you arrive home, the tablet auto-connects to your personal Wi-Fi. Maybe later that day you decide to go to the movies so you pull that iPad of yours out of the backpack to check out reviews.

A Settings app screenshot showing the Personal Hotspot feature toggled on

A Personal Hotspot is prioritized over any public network

Even if there’s a public wireless network available at the theater, your iPad will nevertheless try to prioritize the Personal Hotspot connection through your iPhone. But if you disable Personal Hotspot on the phone, then your iPad will connect to a nearby public Wi-Fi network.

TUTORIAL: How to fully disable Wi-Fi and Bluetooth on iPhone for all networks and devices

iOS saves credentials for public networks, but captive networks (aka subscription networks or Wi-Fi hotspots) are an exception because they block access behind a signup webpage.

The scoring system

We said that iOS’s algorithm starts with the most preferred wireless network, followed by your saved private networks, then any available public ones.

To improve accuracy and reliability, your known networks—that is, any saved networks you connected to in the past—are “scored” based on your actions.

  • Score increases: If you manually switch to a network, its score increases.
  • Score decreases: If you manually disconnect from a network, its score decreases.

The scoring system provides iOS with necessary intelligence in terms of wireless networking that permits it to more accurately prioritize any wireless networks it should join automatically.

We’ve already established that the algorithm assigns higher scores to your most preferred networks. With that in mind, the inevitable question arises: what exactly happens if the device finds multiple wireless networks after evaluating the above criteria?

In that case, iOS prioritizes Wi-Fi networks based on their security level:

OrderNetwork CategoryNetwork Security

But what about multiple networks of identical category and security level?

I thought you’d never ask… In that case, iOS picks the Wi-Fi network identified as having the strongest received signal strength indication (RSSI), according to Apple’s support document.

Preventing Auto-Join

If you’d like to prevent your iPhone, iPad or iPod touch from automatically joining your previously saved Wi-Fi networks, be sure that the option labeled Auto-Join is turned on when you hit “i” next to the network name in Settings → Wi-Fi.

You can turn off the Auto-Join option for any known network individually in Settings → Wi-Fi

Conversely, leaving Settings → Wi-Fi on ensures your iOS device can remember network and login information, automatically reconnecting to that network when you’re in range.

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