Signal jammer, also known as signal blocker or signal shield, is an electronic device whose main function is to block, interfere, or deceive wireless communication signals by emitting electromagnetic waves of a specific frequency. These devices are typically used to prevent unauthorized wireless communication, protect privacy, or restrict the use of mobile devices in specific situations.

The working principle of a signal jammer is based on transmitting a frequency that is the same or similar to the target signal, thereby generating interference at the receiver end, making the original signal unable to be correctly received and decoded. This type of interference can be broadband or narrowband interference targeting specific frequencies.

In the market, there are various types of signal jammers that can target different wireless communication technologies, such as GSM, CDMA, 3G, 4G/LTE, Wi Fi, Bluetooth, etc. They can be used in various occasions, including but not limited to:

1. Security sensitive areas: such as government agencies, military facilities, prisons, etc., to prevent illegal communication and potential security threats.
2. Exam and academic environment: Used in the exam room to prevent cheating, such as using mobile phones or other wireless devices to transmit answers.
3. Business environment: such as cinemas, theaters, conference rooms, etc., to reduce interference and improve focus.
4. Personal privacy protection: Individuals may use signal jammers to prevent others from tracking their location or preventing unauthorized recording and communication.

However, the use of signal jammers is subject to legal restrictions in many countries and regions. This is because they may not only interfere with legitimate wireless communication, but also have a serious impact on emergency services such as police, firefighting, and medical first aid. Therefore, before considering the use of signal jammers, it is necessary to understand local laws and regulations and ensure that their use does not violate relevant regulations.

At the technical level, the design and manufacturing of signal jammers need to consider interference efficiency, selectivity, power control, and environmental impact. With the continuous progress of wireless communication technology, signal jammers are also constantly evolving to adapt to new challenges and needs.