A system and method for detecting the location of a mobile device within an area, uses a plurality of wireless signals sent to or received by the device to derive a first estimate of the position of the device. This position estimate is then adjusted using a probabilistic model of the area, where the area is divided into zones or regions, and where each region is assigned a weighting according to the probability of the device being located in that region taking account of the prior position of the device. By using the weightings to adjust the position estimate, false or ambiguous position estimates are discounted and the true position of the device is more reliably detected. The method also includes techniques to take account of different wireless characteristics of different devices when each is supplied with the same model.