Wireless multimedia sensor networks (WMSNs) have been proposed for use in many challenging applications, such as military surveillance, wildlife tracking, and security monitoring. Reducing energy and storage space consumption are challenging in WMSNs. To address this issue, the authors propose a novel low-duty-cycle WMSN (LWMSN) based on Wi-Fi. This special WMSN is especially suitable for security monitoring, which involves long invalid times in which humans do not appear in the target area. The LWMSN can be intelligently switched on and off by human detection based on channel state information provided by Wi-Fi products. The authors evaluated their design with a simulation and an experiment. Results show that the accuracy of human detection can be >97% on average. In addition, energy and storage space consumption are reduced by 53 and 40%, respectively.