A method of declaring an emergency condition in a wireless sensor network, the wireless sensor network comprising a plurality of devices (10, 11, 12) including sensors (11) arranged for monitoring at least one living body or other entity, the method comprising steps of: sensing a value of parameter related to the living body by one of the sensors (11) wirelessly transmitting information by said sensor to another device (10) in the network determining existence or non-existence of an emergency condition affecting said living body by using said sensed value or said transmitted information and declaring existence or non-existence of the emergency condition to at least one other device (e.g. 10) in the network. The determining step may be carried out in any of the sensor (11), a coordinator (10) of the wireless sensor network, or a central monitor (12) in communication with the coordinator. The declaring step may be performed by setting a frame control field of a frame-based wireless sensor network to a value predefined as denoting an emergency frame. An acknowledgement frame may be used by the recipient to acknowledge receipt of the emergency declaration, after which an emergency procedure is followed. The emergency procedure can involve, for example, increasing the bandwidth allocated to the sensor so as to ensure reliability of subsequent information from the sensor. The method may be applied, for example, to monitoring of patients in a hospital using MBANs operating in accordance with IEEE 802.15.6.
