No, you really don't but it's not up to me to tell you that. (but auto is rubbish).
Auto in the smart is called 'Softouch' and the semi auto is called 'Softip'.
Adding it involves a trip to smart and throwing a wad of money at them but I will show you how to save some cash fitting it yourself and how to get the coding done cheaply. If you have a 600cc smart, you may find it will work straight away after being modified as a small minority has the coding already in place.
The Smart Auto Gear Selector
The entire unit attached to the gear stick is called the 'SE Drive' and there are 3 types.
Full Auto with Engine Start Button
When smart do the automatic conversion, they remove the soft tip SE Drive and install a soft touch SE Drive.
A new gear knob is fitted with a button on the side, a new accelerator pedal is fitted and a TAN code is
placed into the SAM unit via the OBD socket.
The SE Drive is about £100, the TAN code is about £100, the new pedal is £100
and labour will be another £100. As you can see, it's mounting up in price.
How Am I Going To Save Money?
Simple, we are going to reuse your old SE Drive.