Wireless sensor networks are expected to work for a longtime without replacing the batteries frequently. In critical event monitoring applications in wireless sensor networks only a small number of packets need to be transmitted most of the time, when a critical event occurs in the monitoring area and is detected by a sensor node, a message is needed to be broadcast to the other nodes as soon as possible. After that, the sensor nodes can warn users nearby to flee or take some response to the

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... nt. As sensor nodes for monitoring an event are expected to work for a long time without recharging their batteries, sleep scheduling method is needed during the monitoring process. But they are only significantly reducing the energy consumption and the broadcasting delay increases. The sleep scheduling scheme in this work could essentially decrease the communication latency of alarm broadcasting from any node in WSN and the energy of all of the sensor nodes in the network is fully utilized, which in turn increases the network lifetime.