Fly-On-The-Wall-Arrows

[Akrasia]

This is possibly a stupid and massively unfair idea but how about an arrow that when you fire it at an object (bash) it turns the object into an listening post that relays conversation spoken in earshot of the object through the system window to the person that fired it? Balanced by rarity/price and/or listen check for each message, or a negative AB that makes it challenging to actually get a successful hit, possible spot or search check to notice the object is bugged, etc.

[HalflingPower]

Sounds unscriptable to me, not that I am an expert of any sort.

Plus folk would be able to see an arrow sticking out of a chair very easily..

[The Crimson Magician]

TBH if you are in stealth AND invis, I'm pretty sure that the invis breaks line of sight so you can eavesdrop pretty easily if they don't quaff see invis (not exactly a super common potion drop).

[Daemonic Daz]

Inventive, but I don't think we'll be jumping off our seats to script this sadly.