By default, an Apple Watch collects heart-rate readings every 3-7 minutes. If you’d like to collect data more frequently (every 5 seconds), you can do so from within the Cardiogram watch app or switching the Apple Watch into workout mode. The Cardiogram app does not need to be open on the watch or the phone for data to be collected.
For WearOS devices, you can customize how often Cardiogram collects data by using the Cardiogram Wear watch app. You can also turn on continuous recording by turning on workout mode.
Fitbit watches will generally measure your heart rate every 5 to 20 seconds. Cardiogram will only receive these heart rate readings after your wearable has synced the data with Fitbit servers. If your phone is nearby and connected to your wearable, then your wearable may automatically sync; if not, you may be required to open the Fitbit app on your phone to sync your data to Fitbit. If you do not see any Fitbit data in Cardiogram, or the data only appears after a long delay, please see this article for more information.
Garmin watches will generally measure heart rate readings every 15 seconds. Cardiogram will only receive these heart rate readings after your watch has synced the data with the Garmin servers, so these may arrive in Cardiogram with a delay.