StepsApp uses your iPhone’s built-in pedometer to track your steps. Just put it in your pocket and you should be fine. If you carry your iPhone in your handbag, backpack, baby buggy or put it in your car when driving, the app might not be able to track all of your steps correctly.

Likewise, when you go for a bike ride, your iPhone might misinterpret some of your pedal strokes as steps. 
This happens because pedometers calculate steps based on vibration patterns.

Find here more informations  → https://steps.app/en/blog/tech/how-to-install-and-setup-stepsapp-pedometer-and-step-counter