My parents still use a system of telephone signals to know when to put dinner on for the other one. I always wonder how come they decided on seven rings to mean they are setting off and then 3 rings for when they were 15 minutes away?
Before anyone says, they never use their phone while driving. They used to do this before the days of mobile phones so used to stop at telephone boxes.
With the invention of 1471 it got better as we could confirm if it was the correct person ringing.