About SMS QR Codes
An SMS code encodes an "sms:" link carrying a phone number and, optionally, a pre-written message, so that scanning it opens the phone's native messaging app with both fields already filled in - the recipient reviews it and taps send, nothing more automatic than that. It sits close to the phone number code in spirit, but swaps a live voice call for a quick, asynchronous text, which changes what kind of interaction it actually invites: a text can be sent from a quiet room without anyone overhearing, answered on the recipient's own schedule, and kept as a written record afterward in a way a phone call isn't.
One quirk worth knowing about upfront: unlike the "tel:" and "mailto:" links, which are both formally standardized, the "sms:" scheme has never had quite the same universal, tightly defined specification, and support for pre-filling the message body specifically has historically varied a bit more across phone manufacturers and messaging apps than the more established link types do. In practice, this mostly works reliably on current iOS and Android devices, but it's the one part of this format worth actually testing on a couple of real phones before printing anything at volume, rather than assuming universal, identical behavior the way you reasonably could with a phone number code.
It suits situations where a short, specific written reply beats a phone call or a full webpage visit: a pop-up shop's sign reading "text START to join the waitlist," a parking meter that texts back a payment confirmation code, a community group collecting event RSVPs by having people text a single keyword to a shared number. A food truck might set up a sign pre-filling "What's on the menu today?" so a curious passerby gets an answer without first having to think of the right question to ask, lowering the bar for someone who's mildly interested but wouldn't otherwise bother finding out.
Keep the pre-filled message short, specific, and genuinely written from the sender's point of view rather than yours - a long default message reads as presumptuous, and people tend to delete and rewrite anything that sounds like it was written by the business rather than by them. A single clear phrase, like the food truck example above, works better than a paragraph trying to anticipate every possible reason someone might be texting in.
It's worth thinking honestly about who's actually going to scan this before defaulting to SMS as the obvious choice. Reliance on native text messaging varies noticeably by region and by audience - in some countries and among some age groups, an app like WhatsApp functions as the default way people text entirely, with plain SMS reserved mostly for automated notifications from banks or delivery services. If your audience skews toward an app-first messaging culture, a WhatsApp code may get meaningfully more genuine engagement than an SMS code asking for something that group rarely uses by habit.
There's also a cost dimension worth being upfront about depending on where this is deployed: while receiving a text is normally free, in some countries and on some older or prepaid mobile plans, sending an SMS can carry a small per-message charge, unlike opening a free messaging app conversation. It's a minor detail, but for a genuinely cost-conscious or international audience, it's worth being aware that you're asking them to spend something, however small, to reach you this way.
Test the finished code yourself, on both an iPhone and at least one Android phone, before distributing it widely - confirm the pre-filled text actually shows up in the compose field rather than assuming every device interprets the link identically, since this is exactly the part of the format most likely to behave inconsistently across manufacturers.
A common mistake worth naming directly: sending the recipient's number as a purely local number without a country code, which mostly works fine domestically but can misfire if the code is ever scanned by someone traveling or using an international SIM. Where it matters - a code printed on material with any international reach at all - include the country code the same way you would on a phone number code, since the sms scheme accepts the same international format the tel scheme does.
Where this type genuinely isn't the right fit: anything requiring a real back-and-forth conversation, rich media like photos, or a response that needs to reach more than one person at once. Group coordination, sharing images, or an ongoing support conversation are all handled far better by a proper messaging app than by a single one-off SMS, which is really built for a short, single exchange rather than an extended thread. If the interaction is likely to need more than one or two messages each way, a WhatsApp code or a link to a dedicated chat channel usually serves both sides better than repeatedly re-scanning a static SMS code.