| 摘要 |
A relative movement responsive siren alert including transducer means tuned to approximately 500 CPS, for mounting exteriorly of a surface vehicle and responsive to an audio signal from a siren to produce a fluctuating electrical signal. Amplifier means is connected with the transducer means for amplifying the electrical signal to produce an amplified signal. Frequency shift responsive means is connected with the amplifier means and is operative in response to frequency shift in one direction of the amplified signal to produce a first alert signal and to frequency shift in the direction opposite the one direction to produce a second alert signal. An alarm, such as an indicator light, is connected with the frequency responsive means and is responsive to the first and second signal to produce respective first and second frequencies of light fluctuation so the dirver of the vehicle can readily observe the indicator light to determine whether or not the siren source is moving towards or away from the subject vehicle.
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