Tuesday, June 18, 2024

Smallest FM Audio Bug Spy Device

ashwiniAs seen in James Bond movies, audio spy bugging devices are used by intelligence agents in different parts of the world. These devices can help hear conversations from a distance. Their size is extremely small which helps them fit into a pocket and even inside a pen. 

Similarly, we designed an FM audio bug spy device whose range is up to 1km(or even more). The audio is both transmitted and received via frequency modulation. 

The components listed in the bill of materials table below are needed for this project.

Bill of Materials

FM Audio Spy Bug Components
FM Audio Spy Bug Required Components

FM Spy Bug Transmitter

Audio Spy Bug Transmitter Circuit Diagram
Audio Spy Bug Transmitter Circuit Diagram

The audio transmitter used here has a mic and 3 pins as seen in the above circuit. The Vcc and GND pins are connected to a 3.3V rechargeable battery that powers the transmitter module. The third pin is to connect the antenna for the transmitting range to be extended.  

The case that is being used to place the transmitter in, needs to have tiny holes, such that the mic can capture the sound. In this project, we have used a 3D-printed case by designing it accordingly. 

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Audio Spy Bug Receiver

The RDA5807M frequency modulation chip is as tiny as shown below. An ESP8266 12F chip is needed to drive it; as it works on I2C communication which is the same interface used with the ESP chip. This scans and matches the frequency of the receiver with the transmitted signal.

RDA5807M FM Chip
RDA5807M FM Chip

Since the ESP8266 chip does not have USB ports, an FTDI module is needed to program it for communication. Using the USART serial port to drive the RDA5807M FM chip, we send the command to ESP which further sends the signal to the I2C port of the FM chip. 

To create the program, the radio library is used to drive the FM chip and to be used over I2C. The ESP board in the Arduino IDE needs to be installed, after which the library and programming of the ESP chip can be done. 

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After installing the radio library in the Arduino IDE, Go to Examples and upload the scan code to the ESP chip. 

The ESP chip has to be set in the programming mode by connecting the GPIO 0 to GND and Vcc to 3V of the FTDI module. The GND to GND has to be connected along with the Tx pin to the Rx pin and vice versa before uploading the code.

Fm Receiver with RDA5807M chip
Fm Receiver with RDA5807M chip

FM Audio Bug Circuit Connections 

After the ESP chip is programmed, the modules should be connected. From the circuit diagram, it is seen that the FM audio transmitter module is connected to the battery inside the case as designed in the pic below.

Audio Spy Bug Circuit Diagram
Audio Spy Bug Circuit Diagram

FM Spy Bug Device

Next, the ESP and RDA5807M transmitter chip wires are soldered accordingly. The I2C pins of the RDA5807M chip are soldered with ESP 12F I2C pins. The powering pins are soldered to 3V and Vcc pins of ESP, apart from the GND to GND pins.

RDA5807M Wires Soldered

The antenna is now connected to the FM ANT pin of RDA5807M. Two microsized speakers are connected to the RDA5807M L & R audio pins.

After all this, we fit it inside the enclosure.

Programming Audio Spy Bug Device

Function perform on FM audio receiver chip by sending the command over ESP
Functions perform on FM audio receiver chip by sending the command over ESP
Programming Audio Spy Bug Device
Programming Audio Spy Bug Device

Spy Bug Device Programming

Download FM Audio Bug Spy Device Source Code

The audio transmitter FM device is powered-on and hidden in the desired location. The ESP and FM radio receiver device are plugged and the serial port is opened. After scanning the range of FM channels, the channel for the right frequency is selected. 

In other words, this means, the FM channel of the audio bugging device is selected, and you can now hear what is being talked about at the place the transmitter is placed.

So now you know how to make FM Bug Device at home. Still, if you face any issues or have any questions, please ask in the comments below.

You can also check our previous DIY audio bug device using GSM Module and Arduino.

Also, you can start conversations with DIYers, electronics hobbyists, and experts using our Forum.

This article is published on 22 July 2022. Recently updated on 10 October 2022

Ashwini Sinha
Ashwini Sinha
A tech journalist at EFY, with hands-on expertise in electronics DIY. He has an extraordinary passion for AI, IoT, and electronics. Holder of two design records and two times winner of US-China Makers Award.


  1. Hi Ashwini I wanna implement the Continuity Tester With A Chirping Sound in our organization of auto components where rejection rate is high in VMC drilling process, I have link of that tester but not able to understand electronics, I wanna ur email & phone so that I can invite u in our organization for help, Surely we will seat with our MD for implementing this project. Pls support



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