A method for activating a node in a Wireless Sensor Network includes detecting and amplifying pulse signals from a base station; determining whether pulses in the amplified pulse signal are valid; and counting valid pulses in three time periods. A target identifier is calculated using a predetermined formula and numbers of the valid pulses counted. Whether the target identifier matches an identifier of the communication system is determined. The communication system when the target identifier matches the identifier of the communication system is activated. The node is also provided.