# Validation of SocialBit as a smartwatch algorithm for social interaction detection in a clinical population

## TL;DR

SocialBit is a smartwatch algorithm that accurately detects social interactions in stroke patients, offering a new tool for monitoring brain health and recovery.

## Contribution

SocialBit is the first validated, privacy-preserving algorithm for real-time social interaction detection in clinical populations, including those with neurological deficits.

## Key findings

- SocialBit achieved high accuracy (AUC 0.94) in detecting social interactions in hospitalized stroke patients.
- The algorithm maintained strong performance in patients with aphasia (AUC 0.93) and across diverse interaction types and environments.
- Patients with more severe strokes engaged in fewer social interactions, as measured by SocialBit and confirmed by human coding.

## Abstract

Social interaction supports brain health and recovery after neurological injury. Yet no validated tool exists for real-time measurement in individuals with and without neurological deficits. We developed SocialBit, a lightweight, privacy-preserving machine learning algorithm that detects social interactions using ambient audio features on a commercial smartwatch. In a prospective validation study, we evaluated SocialBit against livestream minute-by-minute human-coded ground truth in 153 hospitalized stroke patients who wore the device for up to 8 days, generating 88,918 min of observation. In these patients, the stroke severity and cognition spanned broad clinical ranges (NIH Stroke Scale 0–25; Montreal Cognitive Assessment 8–30), and 24 patients had aphasia across diverse subtypes, including severe presentations. SocialBit achieved high overall performance (sensitivity 0.87, specificity 0.88, area under the curve 0.94) and maintained accuracy in patients with language deficits (AUC 0.93). Despite lower temporal sampling, SocialBit produced interaction frequency distributions closely matching minute-by-minute human coding. Performance was robust across environments and interaction types. Of clinical relevance, SocialBit showed that patients with more severe strokes engaged in less social interaction, paralleling human-coded results. SocialBit is an accurate digital biomarker of social interaction with potential applications in remote monitoring and clinical trials.

The online version contains supplementary material available at 10.1038/s41598-026-37746-x.