An apparatus and method obtains positional information about one or more objects in a detection field. An array includes a transmitting element and a plurality of receiving elements. A truncated cross-correlation function may be applied to determine the interval between signals received by a plurality of the receiving elements, thereby to determine an angular position of an object. A warning zone may be defined and it is determined whether an object is within the warning zone. Also disclosed are techniques for stretching received signals, and techniques for obtaining positional information relating to an object using non-Doppler radar.