The 20 MJ-20 is a highly effective ultrasonic jammer. It is designed to protect confidential information during meetings and conversations. It generates a unique ultrasound signal that blocks the microphones within the range of the device without interfering in the conversation. When turned on, the jammer virtually blocks the operation of any device with microphone and which are designed to record or transmit an audio signal. Such devices are: Mobile phones, dictaphones, audio recorders, wired and radio microphones used for eavesdropping, video and audio conferencing systems, GSM microphones, etc.