A security system (SYS) is proposed for a sales facility having at least one first equipment (CP) for issuing a proof of payment for articles and/or services purchased and having at least one second equipment (CTR) for inspecting the proof of purchase, where the first equipment (CP) generates an electronic proof of payment in the form of an identifier (CD) and has a transmitting device (CP-S) that send the identifier wirelessly to a mobile device (M), and the second equipment (CTR) has at least one receiving device (CTR-R) that receives the identifier (CD) wirelessly from the mobile device (M). The first equipment can be a register system (CP), specifically a self-service register system and/or pay station. The second equipment (CTR) can be a control system that can be installed in the exit area of the sales facility, specifically a control gate system (CTR).