Surveillance devices – overview

Cops and intelligence agencies sometimes use hidden physical surveillance devices – such as microphones, cameras, geolocation devices – to spy on individuals or groups doing subversive actions. The purpose of this page is to give a quick overview of these devices by answering the following questions:

Note that our goal is not to describe all of the surveillance devices in existence – such as the ones used to spy on big companies or governments. We are only interested in the devices that we believe to be likely to be used against individuals or groups doing subversive actions. Devices or features that we believe to be unlikely to be used in our context are marked as “out of scope” below.

The information below is based on our own research. We particularly used our list of found devices, and the numerous technical specifications available from our list of companies. This is a quick overview, and each of the topics below could be covered in much more detail. One day, we should publish a more comprehensive zine for this purpose.

When are they installed?

It seems that hidden physical surveillance devices are used by cops when they want to gather intelligence about specific individuals or groups, and traditional methods – physical surveillance, monitoring of phones and Internet connections, etc – are not effective enough.

The devices can be installed for long-term surveillance of a place or a vehicle, in which case they can stay in place for months or years before being removed by the cops – or in some cases, being found by the people under surveillance. They can also be installed for short-term surveillance of specific events.

In many countries, the installation of such devices is regulated by law, and must be authorized by a judge. Of course, as we know, cops often don’t respect the law.

Where are they hidden?

In buildings

Microphones found inside a power outlet in a building in Bologna, Italy, in january 2018

Hidden microphones and cameras can be installed in buildings to record the sound and image of what is happening inside. They can be installed both in personal homes or in collective spaces. Hidden devices have been found inside objects attached to walls, such as electrical outlets, ceiling lights, air vents, power strips, intercoms and electricity meters. Some have been found hidden inside furniture – in an amplifier, a television, or a kitchen hood. One has been found above a fake ceiling. And in one case, a device was found inside a wall – the hole drilled in the wall to install the device had been covered up with mortar.

Surveillance devices can also be installed inside buildings close to the actual place put under surveillance. Typically, such devices are installed behind windows, allowing them to record the image and/or sound of the place under surveillance, of its front door, or of the way leading to it.

In vehicles

Microphones and a GPS tracker found in the fuse box of a car in Lecce, Italy, in december 2017

Microphones and tracking surveillance devices can be installed in all types of vehicles – cars, trucks, motorbikes – to record the sound of what is happening in the vehicle, and its location.

They can be installed in parts of the vehicle accessible from the outside, sometimes attached with magnets. Such hidden devices have been found attached under vehicles, inside a wheel or in the spare wheel bracket, on a rear bumper, behind the horn grid, or behind the vehicle battery ventilation grid.

They can also be installed inside the vehicle. Such devices have been found between the car body and the interior coating, inside the car ceiling – including inside the part of the ceiling that hosts the interior light, in the interior air vents, inside the heads of the passenger seats, or under the dashboard – including behind the speedometer or in the fuse box.


Hidden microphones and cameras can also be installed outside. In urban environements, hidden devices have been found in streets surrounding places put under surveillance, including inside a fake electric box or inside a fake rock. In rural environments, devices have been found hidden in the vegetation.

How do they work?

Power supply

Hidden surveillance devices need a power supply. The power can be supplied either by a battery or by the electrical system of the building or vehicle in which the device is installed. Sometimes, both sources of energy are present.

The devices are not necessarily turned on continuously. Some hidden microphones are able to turn on only when there is noise. Some hidden cameras are able to turn on only when there is movement by using an infrared sensor. Some tracking devices installed on a vehicle are able to turn on only when the vehicle is turned on, or only when it is moving by using a motion sensor. These features are useful both to save battery power if a device is powered by a battery, and to make it more difficult to detect the device.

Out of scope :

  • devices using less traditional power sources, such as Power over Ethernet (PoE)
  • devices using less traditional sensors to turn on only on specific conditions, such as vibration sensors, pressure sensors, magnetic sensors, and “trip wire” sensors

Data collection


Hidden devices can record sound using microphones.

Out of scope :

  • devices that directly wiretap landline phones
  • devices using less traditional sound recording techniques, such as optical microphones, contact microphones and microphone arrays


Hidden devices can record image using cameras. Some devices include infrared cameras, able to “see in the dark”.


The most common way for devices installed on a vehicle to record the vehicle location is by using the Global Positioning System (GPS), allowing them to obtain their own location almost everywhere on the world surface, without transmitting any data. If a device is equipped with a SIM card, it can also connect to the mobile phone network, and obtain its own location using the cell towers it connects to as reference.

Out of scope : devices that send signals on radio frequencies, so that the signals are received by cops nearby (typically following the vehicle placed under surveillance in their own vehicle) and used to estimate the device location.


Out of scope : devices than can be connected to a computer keyboard, or hidden inside it, to record the keystrokes typed on the keyboard.

Data retrieval

Device equipped with a SIM card found in a vehicle in Italy, in august 2019

The data collected by a hidden surveillance device needs to be retrieved at some point by the cops. Data collected by a device can be retrieved through the mobile phone network if the device is equipped with a SIM card. It can also be retrieved through signals sent by the device on radio frequencies. This technique requires that another device, a receiver, is present nearby to receive the signals – the receiver can be hidden in another building or in a vehicle belonging to the cops for example.

Often, devices have an internal memory storage, for example an SD card, allowing them to store the collected data, so that it doesn’t have to be retrieved continuously. When this is the case, the data may be retrieved only at specific moments, for example only when the cops contact the device through the mobile phone network in order to retrieve its data. This feature can make devices more difficult to detect.

Out of scope : devices using less traditional data transmission techniques, such as physically accessing the devices to retrieve their data, transmitting data over Wi-Fi, over Ethernet, or over a direct satellite connection (for example to the Iridium satellite constellation), or using Power-Line Communication (PLC).

How to find them?

Dismantled electrical outlet in which a microphone was found, in Lecco, Italy, in october 2010

First of all, devices can be found by manually searching for them in the place, vehicle, or outdoor environment suspected to contain hidden surveillance devices. If it is suspected that devices were installed recently, it can help to look for things out of place: furniture that has been moved, or parts of walls that have slightly changed color (which could indicate that a hole was drilled and then covered up). It can help to have the right tools, for example to dismantle electrical outlets in a building or to dismantle the interior of a vehicle. If a device is found, it is important not to stop there: others may be present!

Additionally, detection devices can be bought in specialized stores or on the Internet. Such devices include:

  • radio frequency detectors, to detect devices that are transmitting data on radio frequencies at the time of detection
  • camera lens detectors, to detect cameras

Professional equipment – spectrum analyzers, non-linear junction detectors, thermal imaging systems – can be more efficient, but it is very expensive. It is also possible to pay a specialized company to search for hidden devices, but it is also very expensive, and these kind of companies sometimes have strong links with the local authorities.

Out of scope : devices using discovery detection techniques, such as devices using light sensors to detect by themselves when they are discovered and alert the cops of the discovery.