A phone QR code does one thing: a scan opens the dialler with your number already entered. The person taps the call button. No typing, no saving a contact first, no transcription error.
It is the simplest code type on the site, and the mistakes are all in the details.
Where it earns its place
The pattern is the same everywhere it works: somebody is standing in front of a problem and needs a person, now.
- A sticker on a lift, a boiler, a vending machine or a meter
- A "call for service" sign at an unstaffed counter
- A taxi or delivery vehicle, for the passenger who left something behind
- A for-sale or for-rent board
- A parking notice on a windscreen
- A trade stand, where somebody wants to ring you after the show
Compare that to a business card, where the person wants your details saved for later. That is a vCard code, not a phone code.
Get the number format right
Write the number in international form: +66 followed by the number without its leading zero. So 081 234 5678 becomes +66812345678.
This is the single most common failure, and it is nasty because it hides. A locally formatted number often dials fine from a phone on the same network in the same country — which is exactly the phone you tested with. It then fails for anyone roaming, anyone abroad, and sometimes anyone on a different carrier.
Spaces, dashes and brackets are stripped automatically, so type it in whatever format is easiest for you to check against the source.
Landlines, extensions and short codes
- Landlines work the same way. +66 2 for Bangkok, minus the leading zero.
- Extensions are not reliable. Some phones understand a comma or a
pfor a pause before an extension; many do not. If you need somebody to reach a specific desk, use a direct dial number rather than main-number-plus-extension. - Short codes — three, four or five digit service numbers — are often blocked from tel links by carriers. Test before printing.
It dials, it does not call
The scan opens the dialler with the number filled in. The phone does not place the call on its own, and it should not — nobody wants a poster that can ring a number without being asked.
That extra tap is a feature. It lets the person see the number before committing, which is exactly the reassurance a stranger needs before calling a number they found on a sticker.
Print the number as well
Always. Underneath the code, in readable text.
Three reasons: some people want to save it rather than call now; some phones will not scan; and a number printed next to a code is a trust signal — a bare code asking you to phone an unknown party is something people have learned to be wary of.
It costs one line of text and meaningfully raises the number of people who act.
Tell them why they would call
Scan to call is weak. Lift broken? Scan to call maintenance is not. So is Blocked in? Call the driver.
A code with no stated purpose gets ignored. A code that names the problem it solves gets scanned by exactly the person who has that problem.
Where to put it, and how big
Put it where the problem happens — on the machine, on the door, on the windscreen — not at reception where nobody is thinking about it.
Size follows scanning distance: a sticker held at arm length needs about 2-3 cm; a sign read from a metre away needs 10 cm. The print size guide has the rest.
If it is going outdoors or on a machine, use matte material and a higher error correction level. Stickers on equipment take a beating.
Before you print
Scan it with an iPhone and an Android, confirm the number that appears is exactly right digit for digit, and check it dials from a phone that is not on your own network. Full routine in the pre-print checklist.
Make a phone QR code — one field, thirty seconds.