The wireless control of the parking facility via smartphone posed an initial challenge – especially since an underground car park usually does not already have a WLAN network. The solution should also be able to be integrated as a component into the existing parking control system (with legacy architecture and interfaces and corresponding low-level communication protocol) or ordered as an optional product component by building owners. The goal was therefore a modular system for an autonomous ad hoc network. In doing so, and for the registration and deregistration of users, appropriate security guidelines had to be taken into account. A special feature, and therefore an additional challenge, was the colour code interpretation via the smartphone camera: Due to security regulations, it had to be ensured that the user was away from the car park lifting platforms when operating the system. To activate the system, the user has to confirm a colour code by visual contact with an LED. The recognition of the colour codes by the camera had to be reliably ensured across different iOS and Android smartphone models.