Mobile Product Systems & Integrations Engineer

What you’ll own

The connective tissue that makes the Calibrex product work: Firebase/Firestore, Cloud Functions, user and workout data, payments, analytics, reliability, release tooling, and the boundaries between the mobile app, the wearable, and our voice/AI experience. You will be a product engineer first, not a backend engineer isolated from the app. Your systems work should make the athlete’s experience faster, more reliable, and easier to improve.

You’ll work closely with the founder, who owns the overall architecture and core system boundaries, and with our Product Experience Engineer, who owns the mobile experience. You’ll turn technical constraints and product needs into clear, resilient implementations, and use Codex/Claude as a serious force multiplier, not a substitute for engineering judgment.

This is a high-agency role. One week you may be hardening session persistence and Firestore flows; the next you may be tracing an AI/voice failure, improving a device-integration path, building a payments flow, or setting up the observability that catches a release issue before users do.

You should have

Strong production experience shipping consumer-facing mobile or full-stack products, ideally with React Native/Expo and TypeScript
Deep working experience with Firebase, especially Auth, Firestore, Cloud Functions, Storage, analytics, and crash reporting
Strong systems instincts: you can reason about data contracts, state, failure modes, performance, observability, and reliable delivery
Experience integrating external services, APIs, payments, or AI/LLM-powered product features
Comfortable working at mobile/native boundaries and debugging the real-world behavior of a connected product
A track record of moving quickly without sacrificing reliability, security, or maintainability
A practical, disciplined workflow with Codex or comparable AI-assisted development tools; you can move quickly while reviewing, testing, and owning what ships

Nice to have

BLE, wearable, sensor, audio, or background-runtime experience
Expo dev-client or native iOS/Android debugging experience
Experience with voice agents, tool calling, agentic loops, subagents, or second-brain systems
Experience with subscriptions, payments, HealthKit, release automation, or incident/debugging workflows
Startup experience on a small team