"The use of Bluetooth is especially notable because it can capture data and target people with political messages as they travel through a physical space. This practice has jumped to politics from the advertising industry. In one recent example, Bluetooth beacons (the radio transmitters used to track cell-phone users via Bluetooth signals) were found in campaign yard signs [https://mashable.com/article/beacons-location-tracking-repub...]. In another, people were surveilled using these practices when they went to church. Our team has been exploring how this phenomenon—which we term geo-propaganda—has increased."