There are several types of listening devices in the market including radio frequency, hardwired, acoustic audio and optical box. In this article, we will see some of the frequently used listening devices by the investigators of Sydney Pi

Gsm Bugs 

The GSM bugs work in exactly the same way as a mobile phone. And the perpetrator can dial in and listen silently to the conversation from any place in the world. GSM bug is a small box that is hidden in a room or it may be a purpose-built device like a power strip adaptor, main adaptor, a phone charger, or a PC Mouse. These are the daily use objects that one finds in an office but which could have a dangerous secret in them. High-quality GSM bugs are available online and can be bought from high street shops. 

Miniature Voice Recorders 

Miniature recording devices are readily available from online stores and those disguised as credit cards or USB drives are the recording devices designed to be hidden easily or pass undetected by the target. They have limited battery life and storage which limits their use, but in a lot of situations, they can be just the weapon required by an infiltrator while being affordable and providing high-quality audio. 

Mobile Phones As Bugs 

Mobile phones can also be used as bugging devices. They are programmed not to vibrate, show any outward signs or ring as they are being called. They auto-answer and the caller can listen to the conversation within the room. This can either be done on a target phone which the perpetrator keeps somewhere in the area of the conversation being targeted or by sending a text or an email with an attachment which when opened would download the required software onto the target phone. The phone will then be controlled by the hacker, who can switch it on and listen from any other mobile phone anywhere. 

A new type of app has come that uses the microphone of the phone as a covert listening device. They try to show privacy concerns by saying they record only sound patterns, not actual sound or conversations. But the technology is there and it is being used to some extent. 

So while downloading apps you should be careful as you could download Malware and only download from your service providers website for stop also be careful of using Wi-Fi connections. The unsecured network means that someone else could see what you are doing on your phone while using the same network. 

Radio Frequency Transmitters 

It involves keeping a radio transmitter in a room and listening within range with a receiver. They can be incredibly small and concealed in just about anything including skirting boards, plugs, picture frames etc. They are inexpensive and easy to use and you only require the receiver to listen to them. Radio frequencies are released by all spying devices and these may be detected with specialised equipment. 


There are a lot more in this range and to detect listening devices is difficult, especially as technology is advancing and these devices are shrinking in size, making it difficult to spot with the human eye. They are also designed to look like everyday items like cell phones and pens, so people do not consider them suspicious or may not know that they are in their car, office or somewhere else.