Method for monitoring a tire air pressure and/or at least one other tire-specific variable in tires of a vehicle, in particular of a trailer or semi-trailer of a truck, comprising the following steps: 1.1 detecting the tire air pressure and/or the at least one other tire-specific variable with a detection device of a tire sensor in a tire and transmitting signals as a function of the detected variable by means of a transmitter of a control device of the tire sensor to a router in the vehicle; 1.2 receiving the signals transmitted by the transmitter by means of a receiver of the router and storing the variables transmitted with the signals in a memory of the router; wherein 1.3 the router is supplied with electrical power during driving operation of the vehicle via an electrical power connection from an electrical onboard network of the vehicle for receiving the signals and storing the variables; characterized in that 1.4 the router is supplied with electrical power from an energy storage unit of the router outside the driving operation of the vehicle when the electrical onboard network is switched off, wherein the energy storage unit is rechargeable via the electrical power connection when the electrical onboard network is activated, and 1.5 at least even with switched off electrical onboard network and electrical power supply of the router with its energy storage unit a mobile communication device is coupled at least indirectly to an interface of the router for wired or wireless query of the variables stored in the memory, which mobile communication device connects via an internet access to a database with router-specific data and initiates a bidirectional data connection with bidirectional data exchange between the database and the router either via a direct wireless connection between the router and the database or via an indirect connection via the mobile communication device. 1.1 detecting the tire air pressure and/or the at least one other tire-specific variable with a detection device of a tire sensor in a tire and transmitting signals as a function of the detected variable by means of a transmitter of a control device of the tire sensor to a router in the vehicle; 1.2 receiving the signals transmitted by the transmitter by means of a receiver of the router and storing the variables transmitted with the signals in a memory of the router; wherein 1.3 the router is supplied with electrical power during driving operation of the vehicle via an electrical power connection from an electrical onboard network of the vehicle for receiving the signals and storing the variables; characterized in that 1.4 the router is supplied with electrical power from an energy storage unit of the router outside the driving operation of the vehicle when the electrical onboard network is switched off, wherein the energy storage unit is rechargeable via the electrical power connection when the electrical onboard network is activated, and 1.5 at least even with switched off electrical onboard network and electrical power supply of the router with its energy storage unit a mobile communication device is coupled at least indirectly to an interface of the router for wired or wireless query of the variables stored in the memory, which mobile communication device connects via an internet access to a database with router-specific data and initiates a bidirectional data connection with bidirectional data exchange between the database and the router either via a direct wireless connection between the router and the database or via an indirect connection via the mobile communication device.