Privacy policy of the “RudelCash” app
Last updated: 15 November 2026 · applies to the Android app RudelCash (de.christiankempf.rudelcash). The website is covered by the general privacy policy. In case of doubt the German version prevails.
In short: RudelCash stores everything on the event’s devices and only talks to devices on the local Wi-Fi – the other phones, the receipt printers and, if you like, a card terminal; receipt printers can also be connected by USB cable or Bluetooth. There is no cloud, no account with me, no server and no advertising. I receive no data.
Draft note: RudelCash is in development. Before publishing, check against the finished app (TSE connection, licence purchase via Google Play, possibly SumUp) and declare the same in the Play Console data safety form. Remove this box afterwards.
1. Controller
Christian KempfBreitenweg 2, 72406 Bisingen, Germany
E-mail: christian.firmdev@gmail.com
I provide the app. The club or organiser using RudelCash is responsible for an event’s data – such as names on tabs or of helpers; I have no access to it.
2. What the app stores
- Setup: events, price lists and items, tables and floor plan, printers, print groups, ticket layout, devices and their roles.
- Operation: tabs (with a name if you enter one), orders, payments with amount and method, discounts, deposits and stock, plus which device or helper booked them.
- Card payments: amount, result, card type, receipt and trace number from the terminal.
The hub keeps the complete data, each paired device holds a copy. Everything is stored in the app’s storage on the devices.
3. Connection on the local Wi-Fi
The devices of an event connect directly to each other over the local network (TCP, port 47800). Pairing uses a QR code or pairing code shown by the hub; only paired devices receive data. The content is not additionally encrypted on the Wi-Fi – the event’s Wi-Fi should therefore be protected with WPA2 or WPA3. Tickets go to network receipt printers (port 9100); when searching for printers the app queries the addresses in its own network on this port. A receipt printer can also be attached directly to a device: by USB cable (Android asks on the first print whether RudelCash may access it) or via Bluetooth. For Bluetooth RudelCash only lists printers you have paired beforehand in the Android settings; it does not scan the surroundings and does not request your location. Only the content of the ticket goes to the printer. RudelCash sends nothing to the internet.
4. Card payment
If the club uses a card terminal with a ZVT interface, RudelCash sends the amount to the terminal over the local network and receives the result. Only the terminal reads and processes card data; the payment is handled by its payment service provider on behalf of the club. If desired, the receipt printer prints the terminal receipt.
5. NFC, camera and unlocking
With NFC RudelCash reads and writes the stickers on the tables; they only contain a table identifier. The camera is only used to scan QR codes for pairing and at the tables; recognition runs on the device, images are neither stored nor transmitted. Resetting orders and other sensitive steps are confirmed with the device’s screen lock (fingerprint or PIN); RudelCash only receives the result.
6. Export
You can pass on reports and price lists as CSV files via Android’s share function, and import price lists from CSV files. Where they go is up to you.
7. Permissions
| Network | Connection to the other devices, receipt printers and card terminal on the local Wi-Fi (see 3 and 4) |
|---|---|
| Bluetooth (optional) | Printing on a paired Bluetooth receipt printer (see 3) |
| USB (optional) | Printing on a receipt printer on a USB cable; Android asks for each printer (see 3) |
| NFC (optional) | Reading and writing table stickers (see 5) |
| Camera | Scanning QR codes (see 5) |
| Biometrics | Confirming sensitive steps with the screen lock (see 5) |
8. No advertising, no analytics
RudelCash contains no advertising, no analytics tools, no trackers and no crash reporting.
9. Retention and deletion
The data stays on the devices until it is deleted in the app or the app is uninstalled. Retention obligations for till data (for example under the German Fiscal Code) lie with the club. Android may include app data in the personal device backup if this is enabled in the system settings.
10. Your rights
As I receive no data from the app, I cannot provide information about it or delete it; please contact the club or organiser for that. For questions about the app, contact me at the address above. You may also lodge a complaint with a data protection supervisory authority, for example the one responsible for me: the State Commissioner for Data Protection and Freedom of Information Baden-Württemberg, Lautenschlagerstraße 20, 70173 Stuttgart, Germany.