03Studio 9In production
“people cheat to get several free trial classes and there's nothing we can do about it”
the management of a dance studio
A register of the WhatsApp groups that reads nothing.
A dedicated number, a silent member of the class groups, notes who joins and who leaves, and warns the front desk when somebody comes back. Zero messages read, by design.
- From the first file to the written register
- 1 day
- What's left of it today
- 130 groups, 1 760 people, without reading a single message
- First file
- 20 August 2026
See the public mockup ↗ Designed, coded and shipped, solo
Registre des groupes
Studio 9
Lea M. rejoint « Salsa débutants mardi » après l'avoir quitté une fois.
What the sentence meant
In September, someone takes their free trial class and joins the WhatsApp group for that class. They leave it three weeks later. In November, they come back and ask for a trial class again. Nothing links the two sign-ups: the studio knew it was happening, with no way to see it.
How it works
A dedicated phone number is added to the class groups as an ordinary member. It never writes and it reads no message. All it notes is who joins, who leaves, and when.
The number can neither read nor write. This is not a setting somebody could change: for the studio's confidentiality, the software has, by design, no way of reading or sending anything at all in a group.
The register and the booklet handed to the studio are written on 20 August, the day of the first file. The eight days that follow are the days of pairing the number, obtained on the 28th. First production reading the same day: 48 groups in one call, zero errors. The studio then added the number to its other class groups: at the reading of 30 August, 130 groups, 1 760 people, 6 054 memberships.
The one case the register is looking for
The alert arrives whichever way the studio prefers: as a notification on the front desk phone, like those of an installed app, by text message, by email, or only in the dashboard. It says who, in which group, and between which dates.
Registre des groupes · à l'accueil du studio
Lea M. revient dans « Salsa débutants mardi »
Elle avait rejoint ce groupe puis l'avait quitté. 12 sept. → 3 oct.
Elle vient de le rejoindre à nouveau. À recouper avec les présences avant de proposer un cours d'essai.
What the register does not do
- It does not prove that a trial class was used. It records an earlier stay in a group, nothing more: it is a flag for the front desk, to be cross-checked against attendance.
- Somebody determined to start over can get a second SIM card. The setup makes that more expensive, it does not make it impossible.
Who can open the register
No password. The access key travels inside a one-page document, handed to the front desk: you press the button, the browser remembers the device, and from then on the address alone is enough.
A signed link dropped on its own into a conversation ends up travelling with nobody left to say what it opens. Here it never changes hands without the document that says so, and that also gives the steps to take in case of doubt: the key is replaced in a few minutes, and the old one stops working at once.
On the data side, only the name and the dates of passage are kept, erased two years after the last one.
Registre des groupes
Studio 9 · votre accès à la console
Ouvrir le registre
le bouton contient votre clé d'accès
Ne le publiez nulle part, ne recopiez pas le lien dans une conversation. Pour donner l'accès à quelqu'un, transmettez ce document, pas le lien.
Première ouverture
- Appuyez sur « Ouvrir le registre ».
- La console se souvient de cet appareil : ensuite, l'adresse suffit.
- Ajoutez-la à l'écran d'accueil pour l'avoir comme une application.
The result
“There's nothing we can do about it” became: 130 groups on the register, 1 760 people followed as they join and as they leave, and the studio warned, with the dates, the moment somebody comes back. Zero messages read, by design.