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Wi-Fi QR codes: how they work, and what happens when you change the password

· 2 min read

A Wi-Fi QR code lets a guest join your network by pointing a camera at it, instead of typing a password like k7!Rq-29wP. It’s one of the most useful things to put on a café table or in a rental apartment, and it has one habit that catches people out.

What’s inside it

A Wi-Fi code isn’t a link. It holds a short line of text in a format phones recognize, like this:

WIFI:T:WPA;S:CafeGuest;P:espresso2026;;

T is the security type, S the network name and P the password. When the camera reads it, the phone offers to join that network. iPhones have done this from the camera since iOS 11. On Android, the camera app or Google Lens does it on most phones from the last several years.

Why it stops working when you change the password

The password is in the code. There’s no server in between that could be updated: the phone reads the old password off the paper and tries it. Change the password, or rename the network, and every printed copy stops working.

For the same reason, a Wi-Fi code can’t be made “dynamic”. There’s no link to redirect. So plan for replacements:

  • If you change the guest password regularly, print the code on something cheap to swap, like a table card rather than an engraved sign.
  • When you change it, replace or cover every old copy. A dead code next to a working one wastes guests’ time.
  • Print the network name and password in small text next to the code, for the guest whose phone won’t scan.

Is it safe?

Anyone who can scan the code can join the network, just as anyone who can read a password on a card can. That’s the point, but it decides where the code goes.

Use it for a guest network, kept separate from the network your card reader, printers and files are on. Most modern routers can run one. Don’t print the code for your main network and stick it on the fridge.

The code itself is just text. It can’t install anything, and a phone asks before it joins.

Making one doesn’t have to expose your password either. A generator that runs in your browser builds the code on your device. Ours works that way, so the password never reaches us.

Getting the details right

Most failed Wi-Fi codes come down to a typo. The network name is case-sensitive: CafeGuest and cafeguest are different networks. Pick the security type your router uses; nearly every router today uses WPA2 or WPA3. If the network is hidden, the code has to say so, or phones won’t look for it.

Then test the printed code with an iPhone and an Android phone before it goes on fifty tables.

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