A method for identifying a location of a first container within a group of containers, each container (102, 104, 106) comprising a sensor unit, the sensor unit comprising communication means and a movement detector, each container having an identification code, the method comprising: - at least a first sensor unit of the first container transmitting a first message including a first identification code of the first container, using a first type of transmission means, - at least a second communication module - receiving the first message including the first identification code, and - analysing signal strength or transmission power of the received first message to determine that the first container comprising the first sensor unit is in proximity of the at least second communication module, - comparing the received first identification code to a list of stored identification codes, - updating the list of stored identification codes by addition of the first identification code when said first identification code is absent from said list, and - transmitting a second message to a server, the second message including the first identification code for the server to update the location of the first container, using a second type of transmission means, wherein the second communication module is selected from - a second sensor unit of a second container, and the method comprises detecting handling of the first container by a handler using the movement detector, and the first sensor unit obtaining a verified location from a mobile communication device associated with the handler; - a second sensor unit of a second container and the method comprises detecting handling of the first container by the handler using the movement detector, and the first sensor unit obtaining a verified location from a mobile communication device within a range of communication of the first sensor unit; and - a fixed communication module and the method comprises the first sensor unit obtaining a verified location from the second communication module. - at least a first sensor unit of the first container transmitting a first message including a first identification code of the first container, using a first type of transmission means, - at least a second communication module - receiving the first message including the first identification code, and - analysing signal strength or transmission power of the received first message to determine that the first container comprising the first sensor unit is in proximity of the at least second communication module, - comparing the received first identification code to a list of stored identification codes, - updating the list of stored identification codes by addition of the first identification code when said first identification code is absent from said list, and - transmitting a second message to a server, the second message including the first identification code for the server to update the location of the first container, using a second type of transmission means, - receiving the first message including the first identification code, and - analysing signal strength or transmission power of the received first message to determine that the first container comprising the first sensor unit is in proximity of the at least second communication module, - comparing the received first identification code to a list of stored identification codes, - updating the list of stored identification codes by addition of the first identification code when said first identification code is absent from said list, and - transmitting a second message to a server, the second message including the first identification code for the server to update the location of the first container, using a second type of transmission means, - a second sensor unit of a second container, and the method comprises detecting handling of the first container by a handler using the movement detector, and the first sensor unit obtaining a verified location from a mobile communication device associated with the handler; - a second sensor unit of a second container and the method comprises detecting handling of the first container by the handler using the movement detector, and the first sensor unit obtaining a verified location from a mobile communication device within a range of communication of the first sensor unit; and - a fixed communication module and the method comprises the first sensor unit obtaining a verified location from the second communication module.