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the telephone network uses a different type of multi-frequency signaling.

Employed in a variety of use-cases, one common usage of DTMF signaling is in many intercom door systems, where the signal is used to unlock the door remotely.

Multifrequency signaling

Before the development of DTMF, telephone numbers were dialed with rotary dials for loop-disconnect (LD) signaling, also known as pulse dialing.

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