Wireless sensor network systems deploy a dense array of small, low-cost sensors that observe the local environment. The system can be deployed anywhere, even in inaccessible places. This technology can provide real time monitoring for forest fires. Ignition can be determined rapidly, depending on the wake/sleep schedule of the system nodes. This study investigates the coverage and fire detection ability of a wireless network system. Sub-networks in randomly-distributed nodes convert the network from being randomly distributed to being organised, and reduce the operation time and energy consumption of each node. Dividing the network into three sub-networks increases network battery lifetime by 2.7% and increases energy performance by 63% compared to conventional fire detection networks. The proposed network only requires each node to be equipped with a cheap temperature sensor. Analysis of data from multiple sensors can indicate not only the presence of a fire, but also its intensity, behaviour and direction of spread, which can greatly assist firefighting efforts.