A signal from the TV tells each side of the glasses when to turn on and off, showing each eye slightly different images that create the sense of depth.

VOA: special.2010.01.26

Can you teach me how to use the turn signal?

你能教教我怎么使用转向灯吗？

Can 实战 - SpeakingMax英语口语达人

If the temperature drops below a certain level it sends a signal, 'turn on the heat', and that signal stays on until it gets a negative signal to turn off.

如果温度降到一定程度以下时,探测器会发送一个信号,打开加热器,直到加热器再收到关闭的信号,它就会一直开着

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