In this chapter, you learned how to build a spy microphone based on a simple amplified microphone, Arduino, and a microSD card. The spy microphone can be set up to record audio continuously for a given amount of time.

Of course, there are many things that you can now do in order to improve this project. You can, for example, use a battery to power the project to make it autonomous. Then, you just need to place it in a room in which you want to record a conversation and just come back later to retrieve the SD card with the recording.

You can also connect a motion sensor to the project and use that to automatically start a recording when motion is detected in a room in order to intercept conversations with total discretion.

Another interesting project would be to use the audio levels that are sensed by the project to actually start or stop the recording. For example, you could rewrite the software of the project to continuously monitor the microphone and automatically start a recording when a given threshold is crossed, indicating that somebody is speaking. Then, the program could automatically stop the recording once the audio levels are low again.

In the next chapter of the book, we are going to make another useful project for any spy: an EMF detector to detect the presence of a recording device in a room, for example.