TrackCold: Cold Plunge Timer

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Inspiration

Cold showers are easy to start and easy to quit. Every cold-plunge app I tried was a stopwatch with a sticker on it. Nothing was built for how serious practitioners actually train: alternating rounds of cold and heat, custom rituals, and a history detailed enough to be worth keeping. I wanted the cold to become a practice, not a dare.

What it does

TrackCold times multi-round contrast sessions: configurable rounds of cold and heat, your durations, cold-first or warm-first. The complete timer lives on Apple Watch, free, with Water Lock, phase haptics and an Always-On display, and it shows your live heart rate while you are in the water. Afterwards the summary compares your cold-phase and warm-phase heart rate, every session logs to Apple Health, and your Saga charts heart rate, HRV, water temperature and session length over weeks. Eleven Norse-themed quests, from a 7-day Awakening to Mythic, give the streak a spine.

How we built it

SwiftUI on iOS and watchOS, HealthKit for workouts and heart rate, CloudKit for private sync. No accounts, no server reading your data. All monetization runs through the RevenueCat SDK: monthly, yearly and lifetime behind a paywall built in the RevenueCat dashboard, so paywall copy and layout iterate remotely without shipping a build. Trial eligibility comes from RevenueCat's eligibility check rather than hardcoded copy, so the paywall never promises a free trial to someone who already used theirs.

Challenges we ran into

Getting the commerce and HealthKit layers production-grade took several review cycles. The purchase flow gained an explicit confirmation window and automatic retry, the layout was hardened for every device geometry, and heart-rate capture was rebuilt on the correct HealthKit APIs and made free in the process.

Accomplishments that we're proud of

Version 1.1.0 went live on September 19 and took its first ten downloads, in France and the US, within 24 hours, with zero marketing. The free Apple Watch experience is genuinely complete: full timer, haptics, Water Lock, live heart rate. Not a teaser.

What's next

Version 1.2.0 with session editing and retroactive logging is already staged in App Store Connect. After that: duration-progression coaching and a retention pass with session-outcome tracking and a cancel flow that offers pause and downgrade.

Built With

• cloudkit
• healthkit
• revenuecat
• swift
• swiftui
• watchos