I may have been too terse. In more detail, if you want to know if someone tagged your car there is no point in running the scanner when you are out of range of your car. You only need to start scanning when you get in range.

If you start scanning then and find that there are no tags, you only need to keep scanning if there are people around who might be able to sneak a tag on while you are there without you noticing.

Once you get in and start driving you can stop scanning unless your threat model includes people tagging your car in the middle of your trip.