Eli5: How do automated services on phones know what buttons you’re pressing?

Question

I was just refilling a prescription on the automated line and the thought just dawned on me. How do they know what buttons I’m pressing? Sorry if this is really dumb. I understand next to nothing about technology. Thanks

In: 66

Answer 1

Basically the same way that when you hear music being played on the radio, you hear all the different sounds.

Each button has a different sound. You can think of them as notes on a piano.

1 – A

2 – B

3 – C

4 – D

etc.

So then when you are on the call, and lets say you type in your prescription number, your phone transmits those tones (called DTMF) and the other side hears it, and converts it back to the numbers they meant. Then looks up the prescription.

Nowadays with newer technology and digital everything the tones don’t even need to be sent all the time. But that’s how the older technology worked.