  Social networks have an important role in an individual's health, with the
propagation of health-related features through a network, and correlations
between network structures and symptomatology. Using Bluetooth-enabled
smartphones to measure social connectivity is an alternative to traditional
paper-based data collection; however studies employing this technology have
been restricted to limited sets of homogenous handsets. We investigated the
feasibility of using the Bluetooth Low Energy (BLE) protocol, present on users'
own smartphones, to measure social connectivity. A custom application was
designed for Android and iOS handsets. The app was configured to simultaneously
broadcast via BLE and perform periodic discovery scans for other nearby
devices. The app was installed on two Android handsets and two iOS handsets,
and each combination of devices was tested in the foreground, background and
locked states. Connectivity was successfully measured in all test cases, except
between two iOS devices when both were in a locked state with their screens
off. As smartphones are in a locked state for the majority of a day, this
severely limits the ability to measure social connectivity on users' own
smartphones. It is not currently feasible to use Bluetooth Low Energy to map
social networks, due to the inability of iOS devices to detect another iOS
device when both are in a locked state. While the technology was successfully
implemented on Android devices, this represents a smaller market share of
partially or fully compatible devices.
