We will show you how your car can automatically slow down in speed zones.

 It will make your drive easier, more relaxing in ways you can't imagine.
My wife has one, and even though women-hate-gizmos, she uses it every day!

It works ON ANY CAR newer than 2000.

Step 1: Parts list and schematic for Box labeled "2 Instructable"

Parts List:

Buy or build this board I copied from:
(they also give eagle-cad schematic).

The razor board has inputs:
1) Audio
2) +5vDC

The razor board outputs:
TTL levels when the audio is DTMF 0,1,...9,#,*

You will need two relays.
(radio shack Model: 275-001 or anything similar)