A method of operating an acoustic sand detector deployed at a flowline within a flow system, the detector comprising an acoustic sensor and functioning to produce electrical output signals in dependence on acoustic signals detected by the acoustic sensor, the acoustic signals being at least partially produced by the impact of sand particles within the flow on an object is provided. The method comprises estimating the location of particle impacts on the flowline; and weighting the output signals according to the distance between the estimated location and the detector location.