A network of nodes (102, 202, 402), wherein the network is a wireless network in which data is wirelessly transmitted between nodes (102, 202, 402), at least some of the nodes (102, 202, 402) comprising: a transceiver for transmitting and receiving data packets; and data storage for storing a database; wherein at least some of the nodes (102, 202, 402) are arranged such that: if a node (102, 202, 402) generates its own new data element, the node (102, 202, 402) updates its own stored database with the data element, and transmits the data element to at least one other node (102, 202, 402); and if a node (102, 202, 402) receives a data element transmitted by another node (102, 202, 402), the node (102, 202, 402) updates its own database with the received data element; wherein the database stored in each node (102, 202, 402) is in the form of a blockchain, the updating by a node (102, 202, 402) of its own stored database is by adding a block corresponding to the data element to the blockchain database of the node (102, 202, 402), and the transmission of a data element from one node (102, 202, 402) to another node (102, 202, 402) is a transmission of a block corresponding to the data element to be added to the blockchain database of the other node (102, 202, 402); at least some of said nodes (102, 202, 402) comprising a sensor (106, 206) for taking a measurement and being arranged to generate a data element corresponding to the measurement such that the database stored by said at least some of said nodes (102, 202, 402) comprises data elements that correspond to sensor measurements taken by said at least some of said nodes (102, 202, 402). a transceiver for transmitting and receiving data packets; and data storage for storing a database; wherein at least some of the nodes (102, 202, 402) are arranged such that: if a node (102, 202, 402) generates its own new data element, the node (102, 202, 402) updates its own stored database with the data element, and transmits the data element to at least one other node (102, 202, 402); and if a node (102, 202, 402) receives a data element transmitted by another node (102, 202, 402), the node (102, 202, 402) updates its own database with the received data element; if a node (102, 202, 402) generates its own new data element, the node (102, 202, 402) updates its own stored database with the data element, and transmits the data element to at least one other node (102, 202, 402); and if a node (102, 202, 402) receives a data element transmitted by another node (102, 202, 402), the node (102, 202, 402) updates its own database with the received data element; wherein the database stored in each node (102, 202, 402) is in the form of a blockchain, the updating by a node (102, 202, 402) of its own stored database is by adding a block corresponding to the data element to the blockchain database of the node (102, 202, 402), and the transmission of a data element from one node (102, 202, 402) to another node (102, 202, 402) is a transmission of a block corresponding to the data element to be added to the blockchain database of the other node (102, 202, 402); at least some of said nodes (102, 202, 402) comprising a sensor (106, 206) for taking a measurement and being arranged to generate a data element corresponding to the measurement such that the database stored by said at least some of said nodes (102, 202, 402) comprises data elements that correspond to sensor measurements taken by said at least some of said nodes (102, 202, 402).