Wireless Sensors Networks (WSN) have recently been applied in a number of hazardous gas detection applications. The state-of-the-art works make an emphasis on sensing and delivering of alert message over the WSN to an operator. Instead, in this paper, we propose a wireless sensor-actuator system which aims at quick gas detection and immediate isolation of gas leak source. The low power wireless sensor node includes catalytic gas sensors, micro processing unit and wireless transceiver which communicates with wireless actuator using ZigBee/IEEE802.15.4 standard and BACnet protocol. Wireless actuator consists of power management circuit, micro processing unit and gas valve. The experimental results demonstrate the sensor node long lifetime while fulfilling performance requirements, quick detection of a hazardous gas and fast actuation time.