The Arcane Ear is a device which gives you the power to use the sounds of Note blocks as Redstone signals through walls, etc.
With 24 different pitches per block, and five different instrument sounds, that means there can be up to 120 Arcane Ears placed nearby with no overlapping frequencies.
NOTE: The Ear gives only a short impulse as a Redstone signal and you need to tune it like a Note Block.
If you already have the Warded Stone and Doors research, you can build a kind of number lock to open the door. Just use normal pressure plates and place note blocks next to them. Put the equal number of Arcane Ears you need inside and space for a few "AND-Gates". Place Arcane ears inside the house (for example 3), then put the same number of note blocks on different materials outside. Then a mechanism can be constructed wherein the signal of the ears in a special order is required so that both the order the pressure plates are triggered as well as the signal from the note block must be correct in order to open the door. A system such as this would be effective on adventure maps, for example. It can also be negated with an ear / note block cycle, which means all notes will be played all few seconds, and hence the correct notes will be found.
This device, with some intelligent planning, can allow you to send redstone pulses very long distances with very little actual redstone. Just set up a button to a note blocks to play a note. Go out 47 blocks from the note block and place an Arcane Ear which is tuned to that pitch. From there, place a single redstone wire and another note block. Repeat this until you get the distance you want.
"Sound is another aspect of the natural world that could use some study. Maybe it can be harnessed with magic to create a magical sensor of some kind? The Arcane Ear is a device that is capable of detecting the sound emitted from nearby note blocks. If it hears a note it recognizes, it will emit a short redstone pulse. The Arcane Ear needs to be tuned in a manner identical to note blocks; the tone and note it listens for depends on the material it is placed upon."'
Research available after Unified Thaumic Field Theory.