Whether you're securing a corporate boardroom or simply want peace of mind in a private space, knowing how to detect and counter surveillance devices is a practical skill in an era where spy hardware has become cheap and widely accessible.
Here's what you need to know about identifying audio and video threats, and what you can do about them.
A measure against secret audio recordings is difficult to implement if spy devices do not use a radio signal via which they could be located. However, the cheaper devices in particular only have a very small microphone, which must be optimally positioned in the direction of the speaker for good recordings. As soon as other people in the immediate vicinity are also talking and the microphone is pointing towards the ceiling, for example, distinguishing between the conversations is almost impossible. Therefore, you have a good chance of discovering even concealed spy recording devices if they are located in an unusual place. The tidier an environment is, the more difficult it is to hide them. All employees should therefore be encouraged to maintain a certain order in their workplace and define fixed locations for objects. In this way, they can more easily recognize and report unknown objects.
Alternatively, you can create artificial ambient noise, for example, by playing music. The closer a sound source is to a person or the microphone, the more the recording is disturbed. Bluetooth loudspeakers and music tracks that contain a high proportion of speech are suitable for this task. You can also download special apps to generate targeted background noise, generally described by the terms white noise or noise generator. If required, the audio signal can be amplified with external Bluetooth speakers. To test how it works, simply make an audio recording with another smartphone while the app is active on the other device. During the recording, you should position the smartphone in different places to test the effect in the room. Then check the results. But remember: Smartphones today have multiple microphones and are optimized with special software and hardware features to transmit speech as clearly as possible and filter out background noise. These phones are therefore superior to almost all audio spy gadgets. If a smartphone cannot record a call, you’re probably on the safe side.
In professional environments, special hardware can perform jamming functions more effectively. Like the apps, these devices are referred to as noise generators or white noise. These devices are electronics that generate the appropriate jamming signals for microphones and loudspeakers that emit the signal. In some cases, multiple loudspeakers are deployed to cover all directions.
To detect hidden cameras, you must use special devices, usually referred to as camera lens detectors or camera detectors, as shown in this figure.
With these devices, a red laser beam or a focused LED light beam detects cameras through their lenses. This technique exploits the fact that almost all lenses in this category reflect red light very well. The detectors often have an opening with a red light filter to help you detect the reflection.
However, you’ll need a certain amount of practice to recognize these reflections. At the same time, you must ensure that the angle is correct. The detector must be located directly opposite the camera lens. As soon as you shine the light onto the lens at an angle, the reflection can no longer be seen properly. You’ll therefore need a long time to scan an entire room with these detectors, and the smaller the lens apertures, the more time-consuming the search. To better recognize a camera lens, you should switch off other light sources to make the red reflection easier to see.
Cameras use IR LEDs for night vision mode. The human eye cannot see IR light, but most camera lenses are can. Thus, IR enables cameras to take black and white pictures in the dark. The IR light can therefore also be detected with other cameras. Your smartphone is often sufficient for detecting IR light. You can easily test whether your smartphone displays IR light using an IR remote control. Activate video mode on the smartphone, point the remote control at the lens, and press any button. You’ll see a dot on the smartphone display, the IR LED. This test works best when the ambient light is not so bright, but now you know you can use your smartphone to search for hidden cameras with night vision mode in the dark.
GSM listening devices with a mobile phone connection or, in general, all spy gadgets with wireless transmission can be located using their radio connections. The devices for detecting bugs are called bug finders or bug detectors and are offered by various dealers. They receive a radio signal and display the strength on a scale or with multiple LEDs, as shown in the figure below. Some of these devices also beep, which makes it quite easy to locate radio sources without specialist knowledge.
However, as soon as multiple strong radio sources are present, localizing them becomes more difficult. Better equipped devices offer the option of adjusting the sensitivity. This adjustment allows the device to be calibrated to zero in the middle of the room, which can be used to refine the search. Professional devices also provide the option of limiting the frequency to a specific range, which allows you to search directly for Wi-Fi signals, for example.
Countering surveillance hardware doesn't require a background in intelligence work, but it does require awareness. Keeping environments tidy, using ambient noise to defeat audio devices, scanning for lens reflections and IR light to find hidden cameras, and deploying a bug finder for wireless transmitters gives you a layered approach that covers the most common threat vectors. The technology on your side has also improved considerably, as your own smartphone can serve as both a noise generator and a camera detector in a pinch. Stay observant, test your countermeasures, and don't assume a clean sweep is permanent.
Editor’s note: This post has been adapted from a section of the book Hacking Hardware: The Practical Guide to Penetration Testing by Tobias Scheible. Tobias taught and conducted research in the field of IT security at Albstadt-Sigmaringen University for more than eleven years.
This post was originally published 7/2026.