Wireless listening devices can be manufactured from simple household products such as batteries and wires. These items make them easy and inexpensive to manufacture. Due to this reason, many students use these as spy devices. Another interesting fact is that the size of these devices is very small and lightweight.
These items detect sound in rooms that have outside windows. The long distance reach of these devices makes them useful for those doing reconnaissance.
Sonic "Super Ear" Personal Sound Amplifier
What binoculars do for your ears, the Super Ear does for your ears. This device amplifies sound at a distance up to 50 decibels.
Spy Gear Camera
You can set up a spy camera using a hat which is undetectable, lightweight, and easy to make. This allows you to record what the operative or the person you are spying on is up to at all times.