Stabilising a Smart Ring Platform for Women's Cycle Health
Challenge
Plexteq reworked the firmware communication layer and iOS application stack for Australian femtech startup to enable them scale with confidence and accelerate sales.
Key Challenges
- Unreliable BLE Communication Between Ring and iPhone. The ring firmware used a custom Bluetooth Low Energy GATT profile to transmit nightly measurement packets to the iPhone. Under iOS 15+, aggressive background app suspension was silently terminating the BLE central session mid-transfer. The app had no robust reconnection logic, causing partial or lost data syncs - users woke up to empty dashboards despite wearing the ring all night. On iPhone 13 and later models, the system-level Bluetooth permission scoping had also changed, introducing a race condition in the initial characteristic discovery handshake.
- iOS Background Processing and Battery-Draining Polling Loop. The sync architecture relied on a continuous polling timer rather than CoreBluetooth's notification-based characteristic subscription model. This meant the app requested state from the ring every 2 seconds, draining both device batteries and causing the iOS watchdog to terminate the background task before a full night's data - up to 30,000 temperature measurements - could be transferred. App Store reviews consistently mentioned unexpected battery drain and incomplete data, directly impacting ratings and conversion.
- Apple Watch Extension Was Non-Functional Under Real Conditions. Client had shipped an initial Apple Watch companion app, but it relied on WatchConnectivity's interactive messaging mode - a mode that requires the paired iPhone to be in foreground state. In real overnight use, the iPhone was locked and the session consistently failed. Watch users received no morning data at all. Additionally, the watchOS extension was not registered as a HealthKit workout source, preventing HRV data from appearing natively in the Apple Health ecosystem - a key feature demand from the target audience.
Plexteq reworked the firmware communication layer and iOS application stack for Australian femtech startup to enable them scale with confidence and accelerate sales.
Key Challenges
- Unreliable BLE Communication Between Ring and iPhone. The ring firmware used a custom Bluetooth Low Energy GATT profile to transmit nightly measurement packets to the iPhone. Under iOS 15+, aggressive background app suspension was silently terminating the BLE central session mid-transfer. The app had no robust reconnection logic, causing partial or lost data syncs - users woke up to empty dashboards despite wearing the ring all night. On iPhone 13 and later models, the system-level Bluetooth permission scoping had also changed, introducing a race condition in the initial characteristic discovery handshake.
- iOS Background Processing and Battery-Draining Polling Loop. The sync architecture relied on a continuous polling timer rather than CoreBluetooth's notification-based characteristic subscription model. This meant the app requested state from the ring every 2 seconds, draining both device batteries and causing the iOS watchdog to terminate the background task before a full night's data - up to 30,000 temperature measurements - could be transferred. App Store reviews consistently mentioned unexpected battery drain and incomplete data, directly impacting ratings and conversion.
- Apple Watch Extension Was Non-Functional Under Real Conditions. Client had shipped an initial Apple Watch companion app, but it relied on WatchConnectivity's interactive messaging mode - a mode that requires the paired iPhone to be in foreground state. In real overnight use, the iPhone was locked and the session consistently failed. Watch users received no morning data at all. Additionally, the watchOS extension was not registered as a HealthKit workout source, preventing HRV data from appearing natively in the Apple Health ecosystem - a key feature demand from the target audience.
Solution
Plexteq conducted a full technical audit across the firmware GATT implementation, the iOS Core Bluetooth stack, and the Watch extension architecture before writing a single line of new code. The audit identified 14 critical defects and produced a prioritised remediation roadmap tied to measurable stability milestones.
Firmware GATT Profile Redesign
On the ring's nRF52 firmware (C), Plexteq replaced the single GATT characteristic with a chunked packet protocol. Longer negotiated connection intervals cut radio duty cycle, and 7 days of encrypted flash storage cover missed nights.
iOS Core Bluetooth Stack Rebuild
The iOS BLE layer was rewritten around CoreBluetooth's notification model. A three-tier reconnection strategy recovers known devices without rescanning, and a Swift concurrency-safe actor guards the session lifecycle to eliminate race conditions in characteristic discovery on newer iPhones.
Background Processing and HealthKit Pipeline
The iOS BLE layer was rewritten around CoreBluetooth notifications, waking only when the ring signals data.
Apple Watch Companion App - Full Rebuild
The Watch extension was rebuilt as a standalone watchOS 8+ app using WatchConnectivity background transfers, so morning sync data reaches the Watch without the iPhone foregrounded.
Cloud Telemetry and Remote Diagnostics
Plexteq added an IoT telemetry layer: each ring reports packet loss, session duration, reconnections, firmware version, and battery on sync. A real-time dashboard gives the client fleet-health visibility across device generations and iOS versions.
Plexteq conducted a full technical audit across the firmware GATT implementation, the iOS Core Bluetooth stack, and the Watch extension architecture before writing a single line of new code. The audit identified 14 critical defects and produced a prioritised remediation roadmap tied to measurable stability milestones.
Firmware GATT Profile Redesign
On the ring's nRF52 firmware (C), Plexteq replaced the single GATT characteristic with a chunked packet protocol. Longer negotiated connection intervals cut radio duty cycle, and 7 days of encrypted flash storage cover missed nights.
iOS Core Bluetooth Stack Rebuild
The iOS BLE layer was rewritten around CoreBluetooth's notification model. A three-tier reconnection strategy recovers known devices without rescanning, and a Swift concurrency-safe actor guards the session lifecycle to eliminate race conditions in characteristic discovery on newer iPhones.
Background Processing and HealthKit Pipeline
The iOS BLE layer was rewritten around CoreBluetooth notifications, waking only when the ring signals data.
Apple Watch Companion App - Full Rebuild
The Watch extension was rebuilt as a standalone watchOS 8+ app using WatchConnectivity background transfers, so morning sync data reaches the Watch without the iPhone foregrounded.
Cloud Telemetry and Remote Diagnostics
Plexteq added an IoT telemetry layer: each ring reports packet loss, session duration, reconnections, firmware version, and battery on sync. A real-time dashboard gives the client fleet-health visibility across device generations and iOS versions.
Results
Measurable Impact
- 68% Crash rate reduction - App crashes dropped from 4.1% of sessions to 1.3% within 4 weeks of the updated build going live
- 3× Sync success rate - Overnight data sync completion climbed from 31% to 94% of sessions across the active device fleet.
- 4.6★ App Store rating - App Store rating recovered from 2.9 to 4.6 over three months following the stability release.
- 41% 90-day user retention - Cohort retention at the 90-day mark increased sharply as users began reliably receiving complete morning data.
Measurable Impact
- 68% Crash rate reduction - App crashes dropped from 4.1% of sessions to 1.3% within 4 weeks of the updated build going live
- 3× Sync success rate - Overnight data sync completion climbed from 31% to 94% of sessions across the active device fleet.
- 4.6★ App Store rating - App Store rating recovered from 2.9 to 4.6 over three months following the stability release.
- 41% 90-day user retention - Cohort retention at the 90-day mark increased sharply as users began reliably receiving complete morning data.