You can use the Stryd app on your phone to check the level of the battery.
For iOS, follow these steps:
Step 1) Select the Gear Icon in the upper-right corner:
Step 2) Select STRYD from your paired sensors list:
Step 3) Wait for your Stryd to show "connected" to read the most recent battery level:
1. Open up the Stryd App
2. Choose Settings in the bottom right-hand corner
3. If your Stryd is not already paired to the app, please pair your Stryd by choosing Pair Stryd
4. Once your device is paired, stay in the settings page and choose Stryd
5. Once the device connects, under the battery section you will see the current battery level
Contact email@example.com if you experience any problems charging your Stryd.