A jamming transmitter sends a random signal (noise or pulses) with the greatest possible strength at a certain frequency and thus superimposes the original transmission. If jammers are used specifically, they are referred to as strategic jammer. These devices are also known as jammers and the process is known as noise jamming.
Jammers are available for various radio protocols such as Bluetooth, WiFi, GSM, UMTS, LTE and GPS. Whereby the specific frequency of the radio protocols is disturbed. There are very simple and small devices that can only interfere with radio signals within a limited radius. For example, there is a small adapter for the car cigarette lighter with the function of interfering with the GPS signal. Portable devices with an integrated battery have a range of up to 20 meters under optimal conditions, depending on the version. Usually they can interfere with the signals in a room. Powerful stationary devices can have a range of up to 80 meters.
The use of jammers is illegal in Germany. They are primarily used by investigative authorities and the military services. Some of them are used in prisons to prevent illegal communication from prisoners. The challenge here is that no signals from outside are blocked, for example the cell phone signal to call the emergency call. Abroad, jammers are sometimes used in cinemas and theaters so that the events are not interrupted by a cell phone signal. Another use is, for example, the blocking of control signals from drones.
If such a jamming transmitter is used by attackers, it can be used, for example, to block the radio connections of surveillance cameras or window sensors of alarm systems. Therefore, interrupted connections must always be equated with an alarm. In addition, jammers can be detected by continuously testing a radio connection between two components with a cable connection. If the connection is interrupted, a jammer is active. Alternatively, but also more difficult to solve technically, the signal level, the strength of the radio signals, can be tested. If a new strong source is detected here, it could be a jamming transmitter.