This demo presents a privacy-preserving aggregate location monitoring system, namely, TinyCasper, in which we can monitor moving objects in wireless sensor networks while preserving their location privacy. TinyCasper consists of two main modules, in-network location anonymization and aggregate query processing over anonymized locations. In the first module, trusted wireless sensor nodes collaborate with each other to anonymize users' exact locations by a cloaked spatial region that satisfies a prespecified privacy requirement. On the other side, the aggregate query processing module collects and analyzes the cloaked spatial regions reported from the wireless sensor nodes to support aggregate and alarm queries over anonymized locations. The prototype of TinyCasper is implemented on a physical test-bed on the TinyOS/Mote platform with 39 MICAz motes.