You are at the gate, the agent is waving a scanner over your phone, and nothing happens. Your screen dimmed itself to save battery about four seconds ago. That is the single most common reason a boarding pass refuses to read, and the fix takes two seconds: crank the brightness to maximum before you hand the phone over.
Most advice about QR codes is written for the person making one. This is for the person who was handed one.
First work out which direction it points
Before anything else, decide whether you are the scanner or the scanned. It sounds obvious and it causes half the confusion.
Codes you scan with your camera: menus, posters, WiFi cards, business cards, payment requests, package inserts, parcel lockers.
Codes you show to somebody else's scanner: tickets, boarding passes, gym passes, collection slips, return labels. Nothing you do with your own camera helps here, though pointing a phone at your own screen is a common instinct.
If you are scanning and the camera app does nothing, check that QR detection is switched on in your camera settings. It ships enabled on most phones and gets turned off by accident more often than you would think. The basic scanning steps take a minute to confirm.
Read the preview before you tap
When your camera picks up a code, it shows the destination before it opens anything. That banner is the whole security layer, and most people swipe past it without looking.
Look at the domain, not the rest of the address. The real domain is whatever sits immediately before the first single slash. A link reading secure-yourbank.verify-portal.com is not your bank. It is verify-portal.com wearing a costume. Stickers placed over legitimate codes on parking meters, chargers and delivery lockers are cheap to produce and genuinely common, which is why fake QR codes are worth two minutes of your attention.
Two rules cover nearly everything. Do not type a password or card number into a page you reached only by scanning, unless you navigated there yourself first. And treat any code demanding urgent payment as suspect no matter how official the surrounding sign looks.
Tickets and boarding passes
The code holds a booking reference, not your identity. The scanner looks that reference up against a database, which means the code is worthless without the reservation behind it and there is nothing sensitive printed in the pattern.
Before you travel, do three things. Add the pass to your phone's wallet app if the option exists, because wallet passes stay bright and reachable from the lock screen. Screenshot it as a backup so it survives a dead network in a basement gate area. And check whether the venue accepts a screenshot at all, since some ticketing systems rotate the code every few seconds specifically to stop resale, and a screenshot of a rotating code will be rejected.
When it fails at the gate: brightness up, remove any screen protector glare by tilting slightly, and turn off auto-brightness entirely. If the scanner still refuses, the reference number printed underneath can usually be typed in manually. Ask for that rather than starting over.
Invoices and payment requests
Scanning a payment code normally opens either a banking app with the recipient and amount prefilled, or a checkout page in your browser. What you must check is the same in both cases: recipient name, amount, and reference. All three appear before you confirm, and all three are editable by whoever made the code.
Never confirm a payment where the recipient name does not match the business you think you are paying. Invoice interception scams work exactly this way, with a real invoice reissued carrying a swapped code.
If the code opens a page asking you to log in to your bank rather than opening your bank's own app, back out. Real payment codes hand you to an app you already trust or to a payment processor you can recognize by name.
The WiFi card taped inside a rental
A WiFi code carries the network name, the password and the security type as plain text. Scanning it makes your phone offer to join that network, and you tap once to accept. No app, no typing a 24-character password off a laminated card.
Two things to know. On some Android versions you need to open the code from the WiFi settings screen rather than the camera app. And the password sits inside the code in readable form, so anyone who photographs that card has your network. If you own the place, that card belongs on a guest network, not your main one.
Fails to connect? The most common cause is a code generated for the wrong security type, WPA versus open. Reading the code with a scanner that shows you the raw text will reveal the password so you can type it manually.
Two-factor setup codes are the odd one out
This is the one case where scanning with your camera is wrong. A 2FA code shown during account setup must be scanned from inside your authenticator app, not the camera, because the app has to store the secret it contains rather than just display it.
Open the authenticator, choose to add an account, and use its built-in scanner. If you are setting this up on the same device that is displaying the code, most authenticator apps let you paste the setup key that the site shows underneath as text. Take that route rather than juggling two devices.
Save your recovery codes at the same moment. That secret exists in exactly one place after setup, and losing the phone without recovery codes is a painful afternoon.
Menus, cards, and everything else printed
A restaurant menu code usually opens a web page, sometimes a PDF. If it opens a PDF that pinches and zooms badly, ask for a paper menu. That is a failure of the venue, not of you.
A business card code offers to create a contact. Check the fields before saving, because vCards carry whatever the creator typed, including old job titles from a card printed two years ago.
Printed codes fail for boring physical reasons: glare, a fold running through the pattern, ink that has worn thin, a code shrunk too small for the distance you are standing at. Move so the light falls off to one side, back up until the code fills about a quarter of the frame, and hold still for a full second.
If it still refuses after two attempts, photograph it and open that photo in a scanner app rather than fighting the live camera. A still image gives the decoder a much better shot, and the reasons codes stop working are almost always fixable from a photo when they are not fixable live.
