1. A security device comprising: a representation generating unit configured to generate different types of feature vector representations of both visual and non-visual sensory data captured from a location under surveillance; a concatenating unit configured to generate a composite feature vector based on a combination of the different types of feature vector representations for both the visual and non-visual sensory data; a comparing unit configured to compare a sequence of composite feature vector representations of the sensory data with other corresponding sequences of representations of the sensory data captured during a training phase; a generating unit configured to generate, in response to the comparison, a trigger signal; and an anomaly indicating unit configured to generate, via a processor, an anomaly value indicating the difference between each composite feature vector in the sequence and each composite feature vector in the other corresponding sequence, in accordance with the Euclidian distance between the said composite feature vectors, wherein the generating unit generates the trigger signal when the anomaly value is greater than a predetermined threshold, the different types of feature vector representations include a hue histogram feature vector and at least one of a shape descriptor feature vector and motion descriptor feature vector, and the composite feature vector is a combination of at least two of hue histogram feature vectors, shape descriptor feature vectors and motion descriptor feature vectors.