Most spy gadgets that allow you to listen through walls can listen through materials like bricks, wood or any other sound conducive material. The device picks up small sound signals and amplifies them so that you can hear conversations clearly.
You could even use a wine glass and press it to the wall. The cone shape of the wine glass is shaped to pull sound. On the other ear, place cotton wool to remove external noise.
The choices of listening devices are huge: You could use a spy listening device, or you could use a remote listening device or you could use a door eavesdropping device