CUL-01 Ultrasonic Speaker has 33 ultrasonic emitters to avoid unauthorized cell phones to record crucial and confidential information during meetings. It has unattractive appearance and is suitable to be placed in a room or can be portable to work because of its built-in battery inside. The best interfering microphone performance when CUL-01 emitters exactly face a phone speaker because the emitters affects the microphone directionally. Specification Ultrasonic emitters:33 pcs Dimension: 315mm 57mm 55mm Operation time with built-in battery:2.5hrs Remote control to turn on /off the device