Measuring time in the office using bluetooth sensors: Feasibility and validity considerations

The office is a key setting for intervening to reduce sitting, therefore office-specific activity measures are needed to evaluate interventions. We tested whether valid measures of office time and office-specific activities could be obtained using Bluetooth sensing with a variety of sampling intervals, receiver wear positions, and beacon placements. Workers from one building (n = 29, 72% female, age 23–68 years) wore, for one workday, the activPAL3 on the thigh (measured sitting, standing and stepping) and the Bluetooth-enabled ActiGraph Link on the wrist and thigh. Location (office/not) was estimated by Bluetooth signal presence/absence at two beacons in the wearer’s office (desk, wall), with chest-worn video cameras as the criterion. Accuracy in location classification was assessed and compared across 60-s, 30-s, and 10-s sampling intervals. The validity of Bluetooth-derived measures of total time in the office and in office-specific activities was assessed. For both the wrist and thigh-worn Link, with various beacon placements, accurate classification of location (office/not) was obtained, with a significant (p < .05) but trivial difference in accuracy across sampling interval options (F scores all ≈ .98). With the 60-s sampling interval, mean absolute percent error was very small for office time and office sitting time (<5%), but higher for infrequent activities: standing (17%–23%), incidental stepping (30%–49%), and purposeful walking (57%–86%). The ActiGraph Link can be used to validly measure office time and office location of activity with a 60-s Bluetooth setting. Higher resolution improves accuracy but not to a meaningful degree.