A ranger gains the following ability when traveling for an hour or more (Natural Explorer from PH and Unearthed Arcana Revised Ranger, emphasis mine):
Even when you are engaged in another activity while traveling (such as foraging, navigating, or tracking), you remain alert to danger.
What does this mean in the game context, and how should it be interpreted practically for play?
Normally if involved in an activity during travel a character cannot participate in perception checks to, for example, notice when they are being followed.
As adventurers travel through a dungeon or the wilderness, they need to remain alert for danger, and some characters might perform other tasks to help the group's journey.
Characters who turn their attention to other tasks as the group travels are not focused on watching for danger. These characters don't contribute their passive Wisdom (Perception) scores to the group's chance of noticing hidden threats. (PHB p.182-183)
A ranger with this ability may be engaged a travel activity (e.g. foraging, navigating, tracking, creating a map, ...) while still being allowed to participate in the party's perception checks.
You gain the following benefits when traveling for an hour or more:
...
- Even when you are engaged in another activity while traveling (such as foraging, navigating, or tracking), you remain alert to danger.
