A fitness tracker that works with the radio off

Offline is the default, not a mode you switch on

Most fitness apps are a window onto a server. Open one in a dead spot and the exercise search spins, the food database returns nothing, and yesterday's session is a grey rectangle. Some add an offline mode that queues a few actions and syncs them later, which works until the part you needed was the part that lives remotely.

Hejje has no such mode because it has no such dependency. The app reads and writes an encrypted database on the device. A connection is what moves that vault to your other phone; it is not what makes the app work.

What is already on the phone

These ship inside the app on both iPhone and Android. No download step, no first-run fetch, and no degraded version while you wait for one:

• Around 750 exercises, searchable instantly, with sets, reps, weight and estimated 1RM worked out locally.
• More than 13,000 foods, so logging a meal needs no lookup, along with your calorie and protein targets.
• Your entire history: every activity, lift, meal, weigh-in and photo you have recorded.
• Every chart. Streaks, personal bests, weekly totals, muscle balance and weight trends are computed on the device from your own data.
• Kaya, the assistant, which answers from the data already stored there and never sends a question anywhere.

Signing up works offline too

This is the part that usually gives an offline-first app away. Registering asks for a first name and generates a key pair on the phone. There is no address to confirm and no password for a server to check, so there is nothing in the sign-up that has to reach anybody. You can install Hejje on a flight and start recording before you land.

What that buys is covered properly on the private fitness tracker page: no email, no password, no phone number, and a recovery key that is the only way back in.

Recording survives worse than a lost signal

A long run is the hardest thing for a phone to hold on to, and losing signal is the least of it. Android manufacturers kill background tasks aggressively, and a screen that has been locked for two hours is a prime candidate. Recording in Hejje is built to be killed and to come back, so the session picks up rather than ending at whatever minute the operating system decided to intervene.

GPS itself needs nothing from the network. It is a receiver, so your route, distance, pace, splits and climb are all measured the same with the radio off as with full bars.

Maps are where the two platforms differ

Recording a route works offline on both. Drawing the map underneath it does not, and the honest answer is different depending on the phone.

On Android

You can search for a city and download it, and the app keeps up to three regions on the device automatically over wi-fi, refreshing the one you are actually in. When a downloaded region covers your whole route, the map is drawn entirely from the phone with no network request at all.

On iPhone

Hejje draws on Apple Maps, which fetches its tiles on demand. An activity recorded with no signal is stored complete, with every point of the route, and it draws on a blank background until the phone reconnects. Nothing is lost; it just looks bare until it does.

What happens when the signal comes back

The vault syncs itself, sealed on the device first. There is no sync switch to forget, and nothing at the other end that we can read. It is worth knowing both halves of that: once an account exists, everything in the vault goes up, including the sessions you recorded before you registered. Encrypted, but it does leave the phone.

The blog post what our server can actually see goes through exactly what arrives and what it looks like from our side.