Yes. Free, paid for by ads. Nothing to buy. Everything is included — group rides, workouts, smart-trainer control, route planning, turn-by-turn navigation, offline maps, readiness, the Apple Watch app and the web planner. There is no paid tier.
iPhone and iPad on iOS 18.0 or later, and Apple Watch on watchOS 11.0 or later. The watch app is optional — the iPhone app works on its own. Android phones on Android 13 or later. The Wear OS app is still in development and has not been released.
Yes. Kardiacs drives the resistance on smart trainers and treadmills over Bluetooth using FTMS, the standard fitness-machine protocol, so each interval holds its target watts without you touching the trainer. Garmin and Tacx trainers, Wahoo trainers, heart-rate straps and power meters all connect the same way. Save a trainer, power meter, strap and watch together as a kit and they reconnect the moment you start a ride.
Yes. You download the map for your area over Wi-Fi before you leave, and after that the map draws and turn-by-turn guidance keeps calling every turn with no signal at all — on a trail, in a canyon or in a basement. Routing back to your car or your front door works offline too.
Yes, and without any signal at all. In a group ride the phones talk to each other directly — there is no cell service involved, no Wi-Fi network, no server and no account. Unmute the microphone and the others hear your voice; everyone's live position stays on everyone's map. Chat carries text and photos over the same links, and with Voice to Text on, your own phone recognises what you said and sends the words too — so a rider too far back for the voice to reach still reads it. Every message is signed and sealed between the phones that sent them. Voice needs an iPhone 12 or newer on iOS 26.4 or later, paired to each other; positions, chat and photos work on everything else. Like any radio, a group needs at least two devices. Riders can be up to 200 m apart, and further as phones relay it along the group; range varies with terrain.
Nothing. Group rides do not touch a Kardiacs server, because there is no server in the path — the phones are talking to each other. We never see the conversation, the photos or anyone's position, and there is nothing to sign in to. Saved conversations are kept on the phone that saved them, under Preferences, and are never uploaded.
Yes, by saying them. Tap the microphone and talk, and what you said is written down as a note — the gate that locks at dusk, the water at the top, the corner you took badly. It is the same switch the group's microphone uses: in a group what you say goes to the group, and alone it goes to your notepad. You can point the camera at a junction and that is a note too, or type one. Speech is recognised on your iPhone rather than in the cloud, the notes are never uploaded, and you can export the pad to any app or delete the lot whenever you like.
GPS coordinates, planned routes and saved addresses stay on the device — activities sync without their coordinates, and no route, start point or destination is uploaded. Daily readiness is computed on the phone from Apple Health, so nothing health-related leaves it. Playlist generation can be pointed at Apple Intelligence on your own iPhone instead of the cloud, or turned off entirely. The one exception is a group ride: while you are in a group, your live position — and your training numbers, if you share them — go straight to the other riders' devices, encrypted, and never to us.
The Privacy Policy has the full picture.
Yes, and both ways: workouts you recorded in other apps come in, and the sessions you do in Kardiacs are written back out. You can also bring in a ride as a FIT file off a bike computer, import GPX routes, and export any activity as a FIT file to send it wherever you like.
It ties your profile, training history, routes, workouts and gear to an account, so they follow you onto every device you sign in to and into the web dashboard. There is no separate Kardiacs password to create. You can delete the account and everything in it at any time, from the app or the dashboard.
Yes, in the free web dashboard at app.kardiacs.com, in any browser. It holds a route planner that estimates time, work and speed from real elevation gain, head- and tailwind, tire rolling resistance and aerodynamic drag; a zone-based workout builder; your fitness and fatigue history; and the garage of bikes, kits and sensors behind both. Anything you set up there is on the phone at the next sync.
Intervals are stored as blocks of a training zone rather than fixed watts, so a workout resolves against your own fitness — your critical power and W′ — when you ride it. What it suggests each day also reads your recovery: sleep stages, heart-rate variability and stress are tracked alongside your training load, and when you are run down it steers you to an easier route or a rest day instead of another hard effort.
Yes, on the phone or in the web dashboard, down to the interval, the target and the zone. The builder previews the shape and the total, and says plainly when part of a plan is harder than your current fitness can hold. Saved workouts appear in the app's library on the next sync, ready for the trainer to drive.
Kardiacs builds each session its own mix from your own listening, matching each track's tempo to the cadence the interval is asking for — calm warm-ups, driving efforts, easy cool-downs. You can skip, favorite or stop the mix from the phone or the watch, and you can turn the feature off.
Two ways. It is free rather than subscription-funded, and it covers the whole session rather than only the indoor part — the same app runs an ERG-controlled trainer workout in your garage, navigates a road ride turn by turn, and guides a run or a walk. Kardiacs is not affiliated with Zwift, Wahoo, Garmin or Apple.
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