The tracker is designed so that false steps will not be recorded when traveling by car or train. However, if there are constant movements detected by the movement sensor, some "phantom" steps may be recorded. This can happen, for example, when you are in heavy traffic, or on public transport swinging from right to left with the movement of the train. Under these conditions it is preferable to take the tracker off the wrist.
*credit to Sylvain of iHealth Labs EU