SEOUL, South Korea, Jan. 19, 2026 -- Digital healthcare startup 6Letters today announced the official launch of MOJO KING, an iOS application that enables non-invasive monitoring of testosterone-related physiological patterns using Apple Watch data.
MOJO KING leverages heart rate variability (HRV)—a standard biometric signal collected by Apple Watch—to analyze changes associated with male hormonal balance. Without requiring blood tests or external sensors, the app allows users to track hormone-related trends seamlessly in everyday life.
The current version of MOJO KING analyzes individual biometric signals in relation to age-group baselines and 24-hour circadian rhythms. Based on this analysis, users are classified into intuitive categories: "Teto Guy" when values are above the age-adjusted average, or "Egen Guy" when below. Results are presented in a user-friendly visual format and can be easily shared via social media platforms such as Instagram.
With a paid subscription, users can remove in-app advertisements and enable automatic, continuous measurements, allowing them to observe personalized hormone-related changes over time. This supports a shift from one-time readings to longitudinal, trend-based hormone monitoring tailored to individual lifestyles.
MOJO KING is built on a foundation of multiple patents and peer-reviewed scientific research. To further enhance accuracy and personalization, 6Letters is currently training machine-learning models using large-scale medical datasets from the UK Biobank, CDC, Physionet etc. Insights derived from this work will power the next generation of the company's hormone analytics platform.
Notably, MOJO KING goes beyond conventional smartwatch fitness use cases that focus primarily on heart rate and respiration during aerobic exercise. The app introduces a differentiated approach by analyzing pre- and post-changes associated with moderate-to-high-intensity resistance training, offering new insights into hormone-related responses to strength-focused workouts.
Looking ahead, 6Letters plans to expand MOJO KING with additional modes, including hormone-dependent hair loss management and growth-phase optimization. The company is also preparing to launch MOJO QUEEN, a complementary digital health application focused on female hormone analytics.
In parallel, 6Letters is currently conducting a pre-seed funding round at an approximate company valuation of USD 5 billion million. The company expects to complete AI training based on a huge medical data and plans to apply for FDA 510(k) clearance in the first half of 2026, followed by entry into the U.S. Remote Patient Monitoring (RPM) reimbursement market.
MOJO KING is designed to help users understand and manage hormone-related physiological signals in everyday life, said a representative of 6Letters. By combining scientific evidence, large-scale medical data, and wearable technology, 6Letters aims to build a globally scalable digital hormone health platform.
