Fingerprint scanner and headphones: what they have in common

1. Step 1. Fingerprint scanner — uses — Capacitance. A capacitive scanner.
2. Step 2. Capacitance — is used in — Theremin. A hand changes the capacitance of the antenna.
3. Step 3. Theremin — has part — Oscillator. Beat-frequency oscillators.
4. Step 4. Oscillator — is part of — Audiometer. A tone generator.
5. Step 5. Audiometer — has part — Headphones. Headphones.

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