In Chap. 15 , I described a remote DTMF dialer. There, I explained what DTMFDTMF is and how it works. Figures 15.2 , 15.4 , and Table 15.1 show two frequencies are generated on pressing a key of the telephone keypad. Chapter 15 wasn’t concerned with how these tones were generated. There is a massive amount of technical literature on DTMF generation, and I intend this chapter to be something other than a copy or repetition of those techniques. The tones are nothing new; one can even say they are forgotten with cell phones’ market dominance.