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

The heater is on, it's producing heat until a negative signal is registered, 'oh we've gone too high', and then it turns off.

加热器会开着,一直产生热量直到它得到一个关闭的信号,噢我们弄得太热了,然后就关闭了

耶鲁公开课 - 生物医学工程探索课程节选

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

耶鲁公开课 - 生物医学工程探索课程节选