Electronic signal:
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High-frequency squeak, Low-frequency rumble
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Geiger counter
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Transfer, Morse code, reception
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Horrifying throbbing low-frequency rumble
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Interference Broadcasting
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Electronic signal
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Morse code, SOS signal reception
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Radio noise
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Pink noise
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SOS signal transmission, Morse code
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Morse code, welcome
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Low frequency electronic signal
★★★★★