Brass Ear Level 0
Price 1 gp
A brass ear is a short, flared tube with one end narrow enough to comfortably fit against the ear canal. When using a brass ear to listen through a door, window, thin wall, or similar barrier, if the barrier would normally increase the DC of your Perception check to hear sounds on the other side, the DC increases by only half as much as normal.
Source Advanced Player's Guide pg. 249