Another possibility is to use infrared (IR). Since tones are just electrical pulses, you can replace the speaker with an IR emitter and add an IR detector to the decoder.

• 还有一种选择是使用红外线(IR)。即然音频是电子脉冲,你就可以用红外线发射器代替对讲机,并在解码器上加一个红外线探测器。