Using Bluetooth proximity sensing to determine location in a workplace

Most wearable devices that measure sedentary and active time in workplaces cannot determine the context of that time. The ActiGraph wGT3X-BT and Link models allow users to not only measure movement but the wearer’s location relative to a beacon using Bluetooth proximity detection. This function has yet to be independently validated. Knowing where workers are sitting and moving at work can inform strategies suitable for workplace interventions. Twenty-five office workers (32% men, mean ± SD age 39 ± 11 years) wore a wearable camera (video recording) and the ActiGraph Link, initialised as a receiver, attached to the thigh for one work day (6.2 ± 1.1 hours). Link devices initialised as beacons were placed in the entry (n=1), kitchen (n=1), photocopy room (n=1), corridors (n=2?4), and the wearer?s office (n=2). RSSI signals from all beacons were converted to binary outcomes (1=present, 0=absent). Link-determined location was decided using two methods. Method 1: Presence/absence of signal at a single beacon location. Method 2: Signal presence was summed over a 50 s centred moving window for all beacon locations. A single location was assigned based on majority vote and time-use probabilities. Location determined by each method was checked against camera location for sensitivity, specificity and accuracy. Median sensitivity/specificity/accuracy for the office location was 99%/29%/55% (method 1) and 99%/77%/98% (method 2). The median sensitivity/specificity/accuracy for the other locations ranged from 41%/56%/55% (corridors) to 87%/65%/65% (kitchen) for method 1 and 17%/99%/99% (entry) to 83%/99%/99% (kitchen) for method 2. The ActiGraph proximity detection function shows promise as a tool for determining where workers spend time within office-based work settings. When using multiple beacons, a rolling window algorithm that chooses a single location can improve classification accuracy. This information will be for researchers planning workplace sitting interventions.