High frequency signal:
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Low-frequency rumble, high-frequency squeak
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Police radio
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Geiger counter
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Low frequency pulsing and humming signal
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Morse code, reception, transfer
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High frequency squeak
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High frequency signal
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High frequency pulsating electronic signal
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Morse code, SOS signal transmission
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Morse code transmission
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Electronic signal
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Low frequency electronic signal
★★★★★