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Hello @SunsetRunner, have a warm welcome to the Fitbit Community, it's great to have you on board. 
At this moment, the Fitbit app is only able to sync with Fitbit trackers and we do not have any other app that will sync with another wearable device. If you currently don't have a Fitbit tracker you can set MobileTrack in order to count your steps, calories and distance. To set up MobileTrack:
- Open the Fitbit app and tap on Account > Set up a New device
- If your device is compatible, you'll be able to see MobileTrack.
- Tap on it and follow the onscreen instructions.
I hope this can be helpful, give it a try and keep me posted in case you need anything else. 
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