You are right in that it would be realistic. I think wood-elves particularly, with their more acute hearing and vision, should benefit from this skill.

But as with any great idea, it's subject to game balance. There is a risk that it will make them overpowered in the forest.

Rangers can already see hidden and camouflaged characters in their element. What you are suggesting will allow them to possibly sense duo and invis in the forest as well. This will make it especially hard for mages to have a chance in the forest or to pass through undetected.

You can't give them both camo AND the ability to detect everything that is hidden in the forest -- even if it's just dangersense. More often than not, if it's a character that the ranger cannot detect -- it's usually a mage. What this skill would really get at is improved invis and duo, which would not be fair without a huge cost to the ranger.

Just as the element of surprise is crucial for rangers, you have to give their foes some kind of chance to get in and out of forest areas undetected. Mages are one type of foe that rangers can easily pick off in the forest with a successful ambush. That in itself is just nasty. Rangers are a huge concern for any class throughout the ranking phase. Mages suffer through great risk before they can get to a point where they match up against rangers in wilderness areas (i.e. invokers with improved invis using avalanches, or trannies popping out of duo to use various disruptions). To get to that point, mages often must practice, obtain preps, or rank in wilderness areas.

If anything, you'd have to put a huge lag or cost to the skill. Perhaps it forces you to stay in one spot and "listen", which takes some time. Or, make it force you out of camouflage for a short while.

From what I know, Rangers can already snag/trap characters they do not necessarily see. I think that is vicious enough.