A method for detecting the presence of an object in a zone by means of a wireless detector located proximal to the zone, the wireless detector comprising an orientation sensor for sensing the spatial attitude of the detector, the method comprising: defining a solid angle relative to a first spatial reference plane, the solid angle being defined such that at least part of the zone is within that solid angle when the solid angle is projected from the location of the detector; detecting by means of the detector a wireless signal from the object, and thereby estimating the direction of the object from the detector with reference to a second spatial reference plane fixed relative to the detector; sensing by means of the orientation sensor the spatial attitude of the detector; and comparing the solid angle and the estimated direction in dependence on the sensed spatial attitude so as to determine whether the object is present in the zone.