Accessory for use with a smart device and system and method with such an auxiliary device

The invention relates to an accessory for use with a smart device (Smart Device), in particular a smart phone, for operating a vehicle device having a memory unit for storing at least one radio protocol as well as a first interface which is adapted to transmit at least one radio signal, and an antenna arrangement for transmitting and / or receiving radio signals comprising the additional device having a second interface which is configured for establishing a communication connection between the accessory device and said smart device; and the attachment is adapted to receive information from the smart device via the second interface and to send via the first interface control commands, in particular for opening, closing and / or starting of a vehicle on the vehicle device. The invention further relates to a working method with such a supplementary device.