SMS QR code

What is in the code

A URI of the form SMSTO:number:text, or on some platforms an sms: link with a body parameter. Both forms are read by iOS and Android, though individual devices display them slightly differently and a few apps only prefill the number.

The prepared text has a hard practical limit: one SMS carries 160 characters in the Latin alphabet, and anything longer becomes several messages, each charged separately. A message that says what you need in one line is the only kind that belongs in a code.

• Number first, in international format, then a colon, then the text
• Keep the text well under 160 characters
• No quotation marks around the text, they arrive as characters
• One recipient per code, a group message is a different thing entirely

Who pays, and why that matters

On nearly every plan the sender pays, and a reader knows that. It makes a printed code asking someone to send an SMS a request, not a convenience, so the label has to justify it: an entry in a prize draw, a confirmation of an appointment, a report from a location with no data.

Where the reader would pay a premium rate, say so plainly next to the code. A small line of text prevents the kind of complaint that a printed sign cannot answer.

Where SMS still wins

Rural sites, basements, plant rooms, construction hoardings, festival fields: places where a data connection is not a given. Also on very old phones, which is not a hypothetical audience for a landlord or a utility.

For everything else, a chat app or a form is usually better. The reply arrives in a thread, attachments are possible, and nobody wonders what the message cost.

Making it readable

SMS payloads are short, so the pattern stays coarse and scans well even at small sizes. 2.5 cm is enough on a card, 5 cm on a sign read from a step away.

Put the purpose in the label under the code, not into the prefilled text. The reader will edit the text, but the label is what convinces them to scan in the first place.