The technology used in GSM jamming equipment is based on noise attack

Mobile jammers use a technique commonly known as a denial of service attack. Here, the jamming device will emit radio frequencies similar to cell phones, but with more power, thus disrupting communication between the phone and the cell phone base station in the tower.
The idea of interfering by simple circuits (using capacitors, inductors and resistors) is used, which may be simpler, easier to manufacture and generally more economical. Cell phone jamming devices are an alternative to more expensive measures against cell phones, such as Faraday cages , which work best as built-in protection for large structures.