If you use a 3rd-party device/app as the primary data source on Pacer Android, and you find there are steps counted while driving/cycling, please check settings at the data source side.
If you set phone as the primary data source, Pacer Android might count steps while driving/cycling.
The Pacer app will count steps automatically, by using the motion sensor built in device. Sometimes, due to the vibration detected during driving/cycling, the Pacer app counts step.
However, if you want to stop Pacer to count while driving/cycling, you can use the "manually pause" feature.
(Note: The "manually pause" feature is only available on Pacer Android for now.)
See more details here: Pause Button on Pacer Android