Data communication device, having: a computation and data unit (102, 202) which includes a first radio communication module (103, 203) for wireless data exchange with an external radio device (104, 204) or is connected to the first radio communication module (103, 203), a second radio communication module which communicates wirelessly with the external radio device (104, 204), and a memory which stores identification data for the first radio communication module (103, 203), wherein the first radio communication module (103, 203) is operated in a receiving mode in which it is not detectable by the external radio device (104, 204) but, upon receipt of its identification data by the external radio device (104, 204), is ready to establish a connection and ready for subsequent data exchange with the external radio device (104, 204), the second radio communication module is operated in a standby mode in which said second radio communication module waits for a communication query from the external radio device (104, 204), when the second radio communication module receives a communication query from the external radio device (104, 204) and, after establishing a radio communication connection with the external radio device (104, 204), the second radio communication module reads the identification data for the first radio communication module (103, 203) from the memory and sends said identification data to the external radio device (104, 204), characterised in that the data communication device further has: a supply voltage input, a switch-on unit (105, 405) which is coupled to the supply voltage input and has a voltage output connected to the computation and data unit (102, 202), wherein the switch-on unit (105, 405) includes the second radio communication module, when the second radio communication module receives a communication query from the external radio device (104, 204), the second radio communication module causes the switch-on unit (105, 405) to deliver a supply voltage to the computation and data unit (102, 202) via the voltage output in order to activate the computation and data unit (102, 202) and to activate the first radio communication module (103, 203) and switch it to the receiving mode, when the data exchange with the external radio device (104, 204) is completed, the second radio communication module changes to the standby mode. a computation and data unit (102, 202) which includes a first radio communication module (103, 203) for wireless data exchange with an external radio device (104, 204) or is connected to the first radio communication module (103, 203), a second radio communication module which communicates wirelessly with the external radio device (104, 204), and a memory which stores identification data for the first radio communication module (103, 203), wherein the first radio communication module (103, 203) is operated in a receiving mode in which it is not detectable by the external radio device (104, 204) but, upon receipt of its identification data by the external radio device (104, 204), is ready to establish a connection and ready for subsequent data exchange with the external radio device (104, 204), the second radio communication module is operated in a standby mode in which said second radio communication module waits for a communication query from the external radio device (104, 204), when the second radio communication module receives a communication query from the external radio device (104, 204) and, after establishing a radio communication connection with the external radio device (104, 204), the second radio communication module reads the identification data for the first radio communication module (103, 203) from the memory and sends said identification data to the external radio device (104, 204), characterised in that the data communication device further has: a supply voltage input, a switch-on unit (105, 405) which is coupled to the supply voltage input and has a voltage output connected to the computation and data unit (102, 202), wherein the switch-on unit (105, 405) includes the second radio communication module, when the second radio communication module receives a communication query from the external radio device (104, 204), the second radio communication module causes the switch-on unit (105, 405) to deliver a supply voltage to the computation and data unit (102, 202) via the voltage output in order to activate the computation and data unit (102, 202) and to activate the first radio communication module (103, 203) and switch it to the receiving mode, when the data exchange with the external radio device (104, 204) is completed, the second radio communication module changes to the standby mode. a supply voltage input, a switch-on unit (105, 405) which is coupled to the supply voltage input and has a voltage output connected to the computation and data unit (102, 202), wherein the switch-on unit (105, 405) includes the second radio communication module, when the second radio communication module receives a communication query from the external radio device (104, 204), the second radio communication module causes the switch-on unit (105, 405) to deliver a supply voltage to the computation and data unit (102, 202) via the voltage output in order to activate the computation and data unit (102, 202) and to activate the first radio communication module (103, 203) and switch it to the receiving mode, when the data exchange with the external radio device (104, 204) is completed, the second radio communication module changes to the standby mode.