1. A method comprising: obtaining a received signal strength location estimate of a target device based on wireless transmissions made by the target device that are received at a plurality of receiver devices at known locations in a location region; deriving a first search area for the target device based on the received signal strength location estimate; deriving an ultrasound based area in which the target device is estimated to be based on reception by the target device of a particular ultrasound beacon in the location region; computing an intersection of the first search area and the ultrasound based area to produce a second search area; computing a first angle-of-arrival location estimate of the target device in the second search area based on a wireless signal received from the target device at each of a plurality of antennas of the plurality of receiver devices; and computing a location estimate of the target device in the second search area based at least on the received signal strength location estimate and the first angle-of-arrival location estimate.