What the code contains
An SMSTO: link — a number and, optionally, a message:
SMSTO:+491701234567:STOCK 4471The phone recognises the prefix, opens its messaging app and fills both fields. The person can change the text, and has to press send themselves.
The pre-written message is the reason to use one
An SMS code that only carries a number saves a little typing. One that carries a keyword changes what the reply is worth, because the message arrives already labelled:
- STOCK 4471 on a shelf edge — a restock request that names the shelf.
- FAULT M14 on a machine — a fault report that names the machine.
- TABLE 7 in a restaurant — a service call that names the table.
- PLOT 12 on a site board — an enquiry that names the plot.
The sender types nothing and you get structured data. No app, no account, no login, and it works on a fifteen-year-old handset — which matters if your audience is staff on a shop floor or a building site rather than customers with new phones.
SMS or WhatsApp?
They look interchangeable and are not:
- SMS — works on literally every phone, needs no app, no account and no data connection. Costs the sender a message. Best for one-line replies from an audience you cannot make assumptions about.
- WhatsApp — free anywhere including abroad, better for a back-and-forth, but requires the app and an account. Best when the next step is a conversation.
The deciding question is usually whether you want a reply or a conversation. A reply is SMS. A conversation is WhatsApp.
Keep the message short
Every character sits in the pattern. A four-character keyword is essentially free and keeps the code coarse enough to scan off a shelf edge in bad light. A polite paragraph turns the same code into something that needs a bigger label than you have.
If you need the sender to supply detail, ask for it in one short line — "Reply with quantity" — rather than writing it for them.
Where it works well
SMS codes suit places where the person scanning is working rather than shopping: warehouse shelving, plant and machinery, service desks, delivery points, site boards. The common thread is that a short structured reply is more useful than a phone call, and that the people involved may not have your app or want your account.
Test it before you print a hundred
Scan it from a phone that has never messaged you, and check three things: the number is right, the pre-written text arrives intact, and it has not been mangled by an aggressive autocorrect on the way into the composer. Then print.