The utility of bluetooth and smartphone technology to detect peer contact.

= 55; 40% women) completed a 3-week protocol, during which peers carried a small Bluetooth beacon that was detected by participant smartphones. Participants indicated the presence of peers on beacon signal-contingent ecological momentary assessment reports and three daily random reports. Feasibility of participant recruitment was low, primarily due to Android OS updates requiring app revisions that interrupted recruitment. However, feasibility of peer enrollment was high, occurring rapidly but at a lower-than-expected number. Response latencies to signal-contingent and random reports were similar, indicating good feasibility of the ecological momentary assessment report procedures. Acceptability, reflected in high retention for participants and peers, participant self-report ratings, and good ecological momentary assessment report response rates (76%-79%), was high. Functionality was moderate; problems with the app were reported by almost half of participants, and functionality ratings were lower than for acceptability. For validity, the beacon detection technology identified 61% of participant-reported encounters (true positives), with 5.6% false positives. False negatives (39%) were likely due to peer noncompliance or misreporting. Results support the initial utility of Bluetooth-based passive detection for identifying peer presence in real time, offering potential for use in just-in-time interventions targeting health-risk behaviors. (PsycInfo Database Record (c) 2026 APA, all rights reserved).