Ludic Ambiguity on the Wrist: How an "Imperfect" Stress Avatar Becomes a Social Play Mechanic

Wearable biosignals increasingly circulate as social cues, not just personal measurements. We examine StressWatch, a third-party smartwatch app that estimates stress from heart-rate-derived signals and renders it as a glanceable animated avatar on the watch face. Using a multi-method qualitative study—238 App Store reviews, 174 public posts on RED (XiaoHongShu), and 18 semi-structured interviews across North America, China, and Europe—we examine how users navigate the gap between what the system infers and what they feel. We name this gap a playable gap : a space of interpretive openness that becomes a resource for social play. The playable gap supports five recurring forms of everyday play: performative (staging and signaling states), narrative (jokes, folk theories, and collective sensemaking), competitive/cooperative (challenges, teasing, and solidarity rituals), companionship (personification and care), and reflective (micro-experiments and pattern seeking). We argue that, in this case, such biosignal displays function as ambiguity-sustained ludic systems , while also introducing risks around visibility, uncertainty burden, and social pressure. We conclude with design implications for legible uncertainty and consentful sharing.