A technical security device serves to protect business transactions recorded in the cash register against manipulation. The security device can be implemented as a hardware solution (USB stick, SD card) or as a cloud solution. It consists of a security and storage module, as well as a uniform digital interface. When a transaction is entered into the cash register system, data is generated which is then transferred to the technical security device via a uniform digital interface, provided with unique identification features in the security module and stored in a memory module. This way, business transactions are stored completely and tamper-proof via the security device, thus limiting the possibilities of manipulation for cash register operators. Via the digital interface, the stored data can also be returned to the recording system and exported as part of a Cash Register Audit or external audit (Außenprüfung).