This paper presents an overview of our demonstration of a real application of a WSN system for relic protection applied in the Forbidden City of China. We briefly introduce the EasiNet hardware platform we have developed and the corresponding mesh-architecture of the system constructed. We present a sensor deployment optimization tool based on ant colony optimization technology (DT-ACO) to meet the requirements of network connectivity, sensing coverage and a minimized overall cost of the system. We describe a novel power-aware cross-layer scheme (PACS) to facilitate adjustable system lifetime and surveillance accuracy. We also show some detailed results of the application case.