Mobile Product Systems & Integrations Engineer

Mobile Product Systems & Integrations Engineer

Calibrex · New York, NY · In-person · 3 blocks from Grand Central.
Compensation: $100k - $155k + bonus + meaningful equity

At Calibrex, we build an AI voice coach for strength training powered by a magnetic wearable—like GPS for working out that tells you exactly what to do. We’ve shipped thousands of units worldwide, a sold-out pilot, backorders, and real power users. Now we’re building the product systems that let the coach work reliably for every athlete, every workout, and eventually millions of users.

Important: How to get an interview

Send us an email at [email protected] with the following:

• Email subject: Your name | Desired Role
• Your resume/LinkedIn with a brief note on a mobile product or technical problem you’ve owned.
• Include a 3-4 minute video recording (Loom or Gdrive link) introducing yourself and answering:

"You’ve joined Calibrex with the goal of preparing our product systems for one million users. What are the first three things you would examine - in the codebase, infrastructure, or integrations - to assess our readiness, and why did you prioritize those three?"

Submitting a video recording will significantly increase your likelihood of receiving an interview. We prioritize candidates who take this step because it gives us a much better understanding of how they frame problems, establish priorities, and communicate technical decisions.

Don’t worry about production quality or delivering a perfectly polished answer. Thinking out loud is welcome - we want to understand how you think, not how well you present.

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

Who you are

Fitness-first and accountable. You lift weights regularly and take training seriously—this is not a perk box to check. You need to understand the product on your body, care about the moment a system fails in the middle of a set, and care about the athletes we build for.

You move fast, communicate clearly, and prefer owning outcomes over waiting for a perfectly scoped ticket. You enjoy finding the real root cause, make good tradeoffs under uncertainty, and are comfortable getting your hands into unfamiliar parts of the stack to make the product more dependable.