Fitbit Blaze tracker used to have a clockface called 'Zone' that would change background gradient depending on heart rate. I really missed that and made own version called 'Zone Redux'. This clockface changes background gradient in a similar way as original Zone for Blaze tracker. Unlike original Zone clockface, it displays heart rate and date (with day of the week) at the same time instead of toggling between heart rate and date. The clockface also displays a battery charge percentage. It is optimized for battery usage (doesn't update the gradient if pulse didn't change, updates battery only once per minute and more). Supports custom heart rate zones as well. Also recently added vibration on heart rate zone changes as requested by users (enable it in the clockface settings in the Fitbit app).

Troubleshooting:

* Some users are reporting that the background is black and heart rate does not work after a recent update. The issue seems to be that the permissions for the clock face are set to a disabled state. Please go to Clock Faces, click on the Zone Redux → See all details → Permissions and check that toggles on all permissions are enabled.

Explanation for used permissions:

* Activity - needed to access the "body presence sensor", which tells if the watch is on or off your wrist. When the watch is off your wrist, then the code stops reading the heart rate sensor to preserve battery.

* Heart Rate - needed to read the heart rate sensor

* User Profile - used to get the upper/lower heart rate thresholds to determine the heart rate zone for "Vibrate on heart zone change" feature. This clock face works with both: custom thresholds set in the clock face settings and the heart rate zones defined in your profile (Account -> Activity & Wellness -> Heart Health -> Heart Rate Zones). Hence the need for User Profile permission.