A presence detection system for level crossing or to detect a target at the intersection of any paths is described herein. The system comprises an ultrasound sensor array positioned at the intersection of the first and second paths for defining a detecting area thereon and for emitting a first trigger signal when the body is in the detecting area; and a controller coupled to the ultrasound sensor array for receiving the first trigger signal and for emitting an alarm signal indicative of the first trigger signal. The sensor array detects the presence of a target by creating acoustic virtual lines which form between emitter and receiver or transducer and reflectors and/or by deploying conical or parallel detecting beams and which can be used, for example to measure the distance between each sensor forming the array and the target. The sensor array can deploy beams or acoustic lines in several plans and therefore allow detecting penetration above the conventional railway crossing barriers.