Holter Log

A Holter is a heart monitor worn for 24 hours. For it to be useful, the patient has to record when they feel something — a palpitation, dizziness, chest pain, shortness of breath — so the cardiologist can line those moments up against the recording. That is usually done on a paper diary, which is easy to forget, easy to misdate, and easy to lose.

Holter Log replaces the paper. The patient taps a button when a symptom hits; the app stamps the exact time on its own and sends it straight to the doctor’s dashboard.

The patient opens the app with a numeric code the doctor shares, taps Registrar when they feel something, picks one or more symptoms, and optionally adds a note — the timestamp is captured automatically, so there is nothing to write down. Their own history stays visible on the device.

The doctor signs in to a dashboard of patients — each with their access code, when the Holter was placed, how many events were logged, the last event, and whether the exam is still recording. Opening a patient shows the full event timeline, which can be exported to CSV or PDF for the report.

It is deliberately lean: static HTML, CSS and vanilla JavaScript on the front, Vercel serverless functions for the API, and Supabase (Postgres) for storage — no framework, no build step to babysit. The patient app is a PWA, so it installs to the home screen, opens full-screen, and keeps working if the connection drops in the middle of an exam.

Because it handles health data, security is part of the design, not an afterthought. The doctor area is password-protected with a SHA-256 hash — the password is never stored in clear — and a login returns an HMAC-signed session token that travels on each request instead of the password. The Supabase service key lives only on the server, everything runs over HTTPS, and the data is handled in line with Brazil’s LGPD.

I designed and built the whole thing — the patient experience, the doctor dashboard, the API, the schema, and the deployment — working with my AI agent team. It is the way I build now: I set the direction and own the decisions, the agents do the heavy lifting alongside me, and a real, deployed product comes out the other end.

Holter Log is live on Vercel, with the patient and doctor flows working end to end.