Countersurveillance technologies
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Ultrasonic microphone jammer SEL-324B

SEL-324B  is a high-power microphone (including cell phone microphones) and audio recorder jammer integrated into a common loudspeaker case.  

SEL-324B is a high-power and efficient microphone jamming device due to its thought-out design that includes high-quality directional ultrasonic transducer array that pushes a complex, tailor-made noise waveform on a frequency band that is below human hearing point, but right in the zone of common audio microphone bandwidth, applying a constant noise pressure on the microphone's membrane.

An array of 24 ultrasonic transducers in the SEL-324B are installed inside an off-the-shelf commercial loudspeaker case, providing reliable jamming along a narrow cone-shaped path, which makes it a perfect choice for securing meeting rooms without raising unnecessary suspicion of visitors.

To further increase jamming range and efficiency, the number of ultrasonic transducers can be increased to 48. Can be optionally built with an onboard Li-Pol battery unit, enough to provide 3 hours of continuous operation. Please, send an explicit request for these options during your order.


  • An array of 24 high-quality piezo-ceramic transducers, installed in loudspeaker case unit, controlled by a microchip that automatically shifts the noise signal in time and frequency domains, achieving best possible jamming efficiency and rendering any actual speech signal on the microphone unintelligible.
  • Flexible power supply: device can draw power either from the 220V mains or from a built-in Li-Pol battery, with capacity enough for 3 hours of continuous operation.
  • Easy to use control: can be turned on/off via a button switch on the device, or wirelessly with a special RF remote control.
  • Indicator dashboard: device constantly gathers self-diagnostic and battery charge data and outputs it to an easy-to read LED indicator dashboard on the back panel of the device.

SEL-324B standard package contents:

  • SEL-324B jammer, black color finish;
  • Power supply adapter for 220V mains;
  • RF remote control with spare CR2032 battery;
  • Owner's manual;
  • Cardboard shipping box.
Generated noise frequency bandwidth 24 - 26 kHz
Number of ultrasonic transducers 24 pcs (option to increase to 48)
On/off switch button or RF remote control
Average effective jamming range 4 meters *
Power supply 220 V mains
Continuous operation time unlimited
Operation time from battery unit not less than 3 hours (option)
Time to fully charge battery unit not more than 3 hours
Case material plastic and wood
Overall dimensions specified upon request
Weight specified upon request
Operating temperatures from 0 to +50 °C

* Effective jamming range may vary based on type of microphone of the audio device and its relative position to the jammer.