Security of wireless networks is improved by rejecting traffic from a wireless device located outside a defined spatial boundary. The device's spatial position with respect to the boundary is determined using directional antenna arrays on a plurality of measurement points, and calculating where the vectors intersect. Having thus determined a device's location, access to a wireless network can be denied if the device is outside a predetermined spatial boundary. Or, the device's location inside or outside of the spatial boundary can be used for monitoring a changeable location of one or more client devices in a wireless network, for example as a theft detection or theft deterrent mechanism.