This paper proposes an indoor event detection scheme using an electric wave such as intrusion into home or office. The proposed system exploits an antenna array on the receiver side and detects events such as intrusion using signal subspace spanned by eigenvector obtained by the antenna array. The eigenvector is not based on received signal strengths (RSS) but on the direction of arrival (DOA) of incident signals on an antenna array. Therefore, in a static state, the variance of the eigenvector over time is smaller than that of RSS. The eigenvector changes only when the indoor environment of interest changes statically or dynamically. The installation cost is low, because the detection range is wide owing to indoor reflections and diffraction of electric wave and only a pair of transmitter and receiver are used. Experimental results reveal that the proposed method can distinguish the state when no event occurs and that when an event occurs clearly. The proposed method has a superior detection performance to the event detection method based on RSS.