  Reconfigurable intelligent surfaces (RISs) have flexible and exceptional
performance in manipulating electromagnetic waves and customizing wireless
channels. These capabilities enable them to provide a plethora of valuable
activity-related information for promoting wireless human sensing. In this
article, we present a comprehensive review of passive human sensing using radio
frequency signals with the assistance of RISs. Specifically, we first introduce
fundamental principles and physical platform of RISs. Subsequently, based on
the specific applications, we categorize the state-of-the-art human sensing
techniques into three types, including human imaging,localization, and activity
recognition. Meanwhile, we would also investigate the benefits that RISs bring
to these applications. Furthermore, we explore the application of RISs in human
micro-motion sensing, and propose a vital signs monitoring system enhanced by
RISs. Experimental results are presented to demonstrate the promising potential
of RISs in sensing vital signs for manipulating individuals. Finally, we
discuss the technical challenges and opportunities in this field.
