heyday

Inspiration

I've always journaled, in my Notes app or a paper diary, and I've always forgotten to. One night I thought: what if my journal just called me? But, picking up a call takes no willpower. In fact, I've realised that I verbalise a lot better when speaking as opposed to writing.

Our take on Navigation

The hardest place to find your way is inside your own mind. Each call is a moment to take your bearings: say what happened, name how it felt, decide what's next. Over weeks, your pages become a map of where you've been, so you can see where you're heading.

What it does

heyday navigates you through your own head, one call a night. It rings your real phone at a time you choose. You pick a brain dump or a conversation, and either talk about what's on your mind or take a prompt. When you hang up, Claude turns the call into that day's journal page, in your own words. It comes with a mood emoji, the moments that mattered, and anything you said you'd do tomorrow. Pages build a streak, and you can play back any call. You can share the app with your friends and you'll be able to see their streak on a leaderboard! Every month, you get a wrapped, like spotify wrapped, which tells you ket stats like how many hours you spent calling the agent, what topics you touched on the most, how you changed over the month etc. You can also share a day's entry with the friends you choose, inside the app.

How we built it

Claudia did most designing; Eddie did the backend wiring

App: Expo (React Native)
Calls: ElevenLabs voice agents on a Twilio phone line, with Claude Sonnet 5.5 holding the conversation. It answers in about a second, with Claude Haiku as a backup.
Writing the page: Claude Opus turns each transcript into a structured entry.
Backend: Supabase for data and call recordings, plus a small Node worker that places the calls and writes the pages.

Challenges we ran into

Making a call feel human. The agent sounded robotic and unnatural at first. We did a lot of prompt engineering to make it
Verification codes that wouldn't send. US carriers block texts from unregistered numbers. We switched to Twilio Verify and routed it through our own server, so no secret key ever lives in the app.
iMessage or phone calls? We built toward both, then cut iMessage. It added a second surface without making the experience better.

Accomplishments that we're proud of

We shipped a product that actually works, end to end: a real phone rings, you talk, and a page appears. It was the fastest build cycle either of us has had, and the design is polished down to the onboarding.

What we learned

Knowing when to drop an idea, when to push on, and when to double down. We cut iMessage and parked a list of add-ons so we could make the core loop feel great. We also got much better at building with AI tools.

What's next for HeyDay

Summaries: a quick AI summary of each entry at a glance.
Memory: a more sophisticated and refined memory system to store each user's context without bloating the context window of the voice agent