This paper explains our proposed wireless security and monitoring system using array antenna, referred to as array sensor. The proposed system exploits an antenna array on the receiver side and decomposes received signals into eigenvectors and eigenvalues. The proposed system uses these components depending on its applications, such as intrusion detection, monitoring, and passive localization. When an event (e.g. intrusion) occurs, the propagation environment changes, and thus the eigenvector changes. Based on the change of eigenvector, we can detect an event accurately. Using machine learning based on these components, the proposed system can classify several more complex states and activities. This paper introduces the fundamental principle of the proposed system and its various applications.