This is an easy and cheap way to bring some spy tech into your life. Most of the items you already have at your home or can be bought at your local thrift store/flea market/yard sale. The key item is the baby monitor. It can run off ac or battery power, has wireless, and is pretty sensitive. I chose a trashcan because it would not look odd in any room and most people don't go digging around in them.
Disclaimer: This device is for entertainment only. Please do not break any laws.
Step 1: Tools/Materials
Most of the tools and materials you either have right now or can easily get.
Baby Monitor (You can find these at thrift stores or yard sales. Especially ones that sell baby stuff.)
Step 2: Take the Baby Monitor Apart
Remove all the screws from the baby monitor until you have just the circuit board and all the wires.
Step 3: Remove the Extra Parts
Cut the wires for anything that is not needed for the functioning of the microphone. I removed the screen, temperature sensor, and light switch. Tape off any exposed wires so you don't have any shorts.
Step 4: Prepare Trashcan
Select a trashcan and put a hole near the top for the microphone to be placed near. You need the hole so that sound can easily reach the microphone. I think that given the sensitivity of the microphone you should be able to hear if you opted to not put a hole.
I used a knife to make the hole. Be careful you do not cut yourself.
Step 5: Install Listening Device in Trashcan
I used duct tape to attach the listening device to the trashcan. Be sure to place it so that the trashcan is not top heavy and prone to tipping. I made sure the battery was at the bottom. The extra weight kept it stable. Once in place, put in a trash bag. The device should be well hidden. Now you are ready to spy.
Step 6: Alterations/Additions
You could place the device inside other objects if you want. It would easily fit behind a picture frame, inside a couch cushion or under a table.