A system used in touch-tone telephones. DTMF assigns a frequency to each key for easier identification. In spy world for example, DTMF technology is used in tone decoders. It lets you recognize the numbers dialed from a phone. You can find out what number was dialed. All you need to do is play the pre-recorded tape (any audio) and the dialed numbers appear instantly on LCD screen of a DTMF decoder.
DTMF is also knows as touch-tone. If you’d like to see what frequencies are used for DTMF technology, here’s a simple table that shows you:
You see that there’s low and high frequency numbers in the table. Using two frequencies helps preventing signal misinterpretations.