How do hidden spy cameras work?

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Aina Prat Blasi
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A hidden surveillance camera gives you the ability to remotely monitor your home or apartment through a simple mobile application installed on your smartphone. Hidden cameras are also known as spy cameras and their main purpose is to record people without their knowledge. But how do hidden spy cameras work? Let's find out!

How do hidden spy cameras work?

So how do hidden spy cameras work? A hidden spy camera broadcasts video using wireless transmission to send and receive an image. First, it detects the image through the lens and then transmits it with the help of a radio transmitter in the form of a radio signal on a particular frequency to the device where the image is displayed on the video screen.

When we use the term “hidden camera” it means that the camera is not visible to the subject being filmed. For this reason, these cameras need to be tiny and inconspicuous. If you want to know more about hidden spy cameras and their features, keep reading this article.

The basics: principle of operation

The wireless spy cameras have a radio control, thanks to which they are able to communicate with a wireless router or an Internet box. The camera, therefore, belongs to the home computer network, just like a tablet, computer, and other game consoles. This wireless link gives the user the ability to connect to the camera remotely. In practice, it is usually sufficient for the user to install a mobile application on his smartphone.

Step by step guide on how hidden spy cameras work

When the user is at work, on vacation or traveling, the app connects to the camera wirelessly via the internet connection in your home. Once communication is established, the user consults live the images sent by the camera. It also accesses functions such as zoom, lens shift or night vision activation if your device has them. At the same time, it can remotely control the recording of images captured by the camera, both directly inside the camera (by adding a microSD memory card), and on your phone.

Since the wireless spy camera relies on your home's Internet connection to send images, you cannot connect to it if there is no Internet. The quality of the transferred images also depends on the Internet connection (upload capacity, i.e. data transmission) as well as the bandwidth of the local wireless network.

Keep in mind that hidden spy cameras can also record audio.

How a hidden spy camera is composed

Each hidden spy camera consists of these 3 components:

The camera

A hidden spy camera can be wireless or wired. Their primary purpose is to capture footage of the area being monitored. The wireless hidden camera transmits a video signal to a receiver where the image is recorded or just displayed. Wired hidden cameras are connected by a cable.

Recording device

A recording device is used to archive footage recorded by a hidden spy camera. Most recordings are stored on the internal hard drive or micro SD card supplied with the camera.


The monitor is the device where you view recorded video or live video. In most cases, the movie is viewed on a mobile phone or on a PC or tablet.

Image transmission and reception process

1. Basics of wireless

Hidden spy cameras use wireless transmission to send and receive an image, which makes them easier to hide and convenient to use. Therefore you don't need to have a cable from the camera to the receiver to get an image, but some models come with a cable because they need to be plugged into a power source in order for them to work.

The wireless hidden camera captures images with the help of light passing through the lens. Light detectors only measure red, green or blue light, so all three photodetectors are combined to display a complete image. Some wireless detectors are equipped with a motor and a motion detector, with which you can follow all movements in the area.

All wireless hidden cameras have a built-in radio transmitter that transforms the recorded image into a radio signal on a particular frequency. That signal can only be transmitted to a receiver inside the building. Then the receiver takes the signal and transforms it back into an image.

The receiver has multiple functions, depending on its purpose. If the wireless spy camera wants to continue surveillance, the image is displayed on the video screen in real time, but the image can also be recorded on a specific storage medium or on a PC hard drive. Today, cell phones are most commonly used to monitor hidden surveillance camera footage.

2. The camera lens

Structurally, the camera lens is a complex system of lenses that are encased in a frame and compensate each other for optical distortion. Collects and projects light energy onto a light sensor to form an optical image.

The main parameter is the focal length (measured in millimeters), which determines the image scale and angle of view. It is the distance from the axis of the lens assembly to focus (the intersection point of the initially parallel rays after passing through the lens). The shorter the focal length, the wider the field of view. The 2,8mm lens provides video surveillance in a sector with a viewing angle of ~ 100º. The more the camera focuses (for example, 8 mm), the smaller the angle of view, but the greater the distance from the observation object necessary for high-quality shooting.

Video surveillance systems have different tasks, so spy cameras use different types of short focus, long focus and ultra long focus lenses: fixed focal length, variable focal length, motorized and fisheye.

3. How are hidden cameras built?

Most hidden (spy) cameras are built into common use items such as alarm clocks, televisions, cell phones, toys, ink pen caps, etc. They are mainly used for home surveillance, but can also be used for industrial espionage. For example, you will use your hidden camera to take a look inside your house during the holidays to verify that no one has entered. For this reason, spy cameras are built into objects that can easily adapt to the home environment so that they are difficult to notice.

4. How to install a hidden camera?

The installation of a hidden camera does not present particular difficulties; you need to unpack the camera, plug or charge it, choose its location, then turn it on and connect it to your home network. This last step is often the most tedious as you need to connect to the camera interface to enter the WEP or WPA security key of the WiFi network. The intervention of a professional is also recommended if you intend to integrate your camera into your alarm system and build a more advanced security system.

  • How to hide a camera in your bedroom?

The technical elements of a spy camera

Image quality: Image quality is determined by the screen resolution.

    • The Sensor: The essential element, positioned behind the lens, that captures the light
    • Brightness (LUX): brightness is expressed in LUX (between 0, total darkness and 50.000 lux).
    • The Lens: Varies according to the desired viewing angle.
    • The different categories of hidden cameras
  • Infrared cameras: At night, they use light-emitting diodes placed around the lens to detect infrared radiation (heat waves) and relay images in black and white.
  • Day / Night Cameras: Automatically switch to day or night mode depending on the light level.
  • Motorized domes (possible rotations) and spy cameras (which blend into the background).

Spy camera resolution table

The higher the resolution of the spy camera, the higher the quality and detail of the image. A resolution of 2 megapixels (Full HD), which is supported by most modern monitors, is often sufficient.

The most common resolutions are:

  • HD (720p) - 1280 × 720 (1 megapixel) - medium resolution, suitable for general assessment of the area of ​​interest.
  • SXGA (960p) - 1280 × 960 (1,3 megapixels) - increase the number of pixels vertically for a specific scene.
  • Full HD (1080p) - 1920 × 1080 (2 MP) - resolution with the ability to identify a person.
  • Quad HD (1440p) - 2560 × 1440 (4MP) - Improved details for moderate bandwidth requirements.
  • 5 MP - 2560 × 1920 (5MP) - High details, sharp images.
  • 4K Ultra HD (2160p) - 3840 × 2160 (8MP) - excellent image quality, digital zoom capability.

With the development of digital technologies, the trend towards increasing the number of effective pixels is growing, although high resolution is only relevant for objects where it is necessary to clearly see the denomination and number of a banknote, recognize a license plate at a large distance and constantly resize the image.


1. Can hidden cameras record audio?

Hidden spy cameras can be equipped with one or more audio inputs and outputs, so they are capable of recording audio. Some models have a built-in microphone, but if required, a professional omnidirectional or unidirectional microphone can be connected to each spy camera with audio input (depending on the application).

2. How long can hidden spy cameras record?

Hidden spy cameras have an average recording time of 60 minutes. This depends on the capacity of the built-in battery. Some spy cameras come with a cable so they can be plugged into an electrical outlet.

3. Can spy cameras record in low light conditions?

Yes, the hidden spy cameras have a night vision mode which allows them to record even in low light conditions and during the night. The night vision mode is activated automatically when the camera sensors detect a dark environment.

4. How many videos can hidden spy cameras store?

It depends on the internal memory and external memory (SD card) that a hidden spy camera has. If the spy camera has the ability to use SD cards, the 256GB will be more than enough to record many hours of footage.

The best 5 spy cameras

# Preview Product Vote Price
1 Spy Camera, 1080P HD Hidden Camera Wifi Wireless Microcamera for Home Long Life ... 355 Reviews 49,90 EUR Buy on Amazon
2 THEXLY Mini Hidden spy camera HD professional wifi - Square spy cam indoor surveillance ... 17 Reviews €39,99 €24,99 Buy on Amazon
3 Spy Camera Indoor Wifi 4K HD Mini Hidden Camera Wireless Microcamera Camcorder ... 98 Reviews 49,99 EUR Buy on Amazon
4 Wi-Fi Camera Indoor, HD, Outdoor, Mini, Hidden Camera, Wifi, Wireless, Night, ... 75 Reviews €49,90 €44,90 Buy on Amazon
5 Mini Spy Camera, Gutkam Full HD Hidden Spy Camera with Vision ... 223 Reviews 24,99 EUR Buy on Amazon

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