The security of the physical layer promises to provide secrecy for wireless communication. The chaotic direct sequence spread spectrum (chaotic-DSSS) is one of the distinguished techniques for providing secrecy in wireless communication. However, conventional chaotic-DSSS requires chip synchronization which makes this system complex to implement in wireless sensor networks (WSNs). This letter suggests using a fix chaotic-DSSS and also proposes a new method, called fake users, to enhance the security of the chaotic-DSSS based WSNs. The performance of the proposed method is theoretically investigated and validated through simulation. The results suggest that the proposed method can significantly improve the security of WSNs.