I lost my backup key for my Mitsubishi car and wanted to replace it. To get a cheap solution I had to remove the transponder from the key and go for a walk to the city.
To get a spare key from the manufacturer, you’d have to pay 140 € – and that is not including the programming costs of the keys transponder (> 25 € extra). Third party resellers offer key replication for 69 €, but demand programming the new key transponder on site, very far away from my place.
These options were too expensive for my taste, so I decided to remove the transponder from the key case and to permanently attach it close to the keyhole in the car.
The exact position where the transponder is being attached can be very specific. In my case (Mitsubishi Colt VI, should be the same for Smart Fortwo/Forfour and similars) it was just a tiny area that was doing the job. The right portion can be checked by the cars engine immobilizer indication light in the instruments. Once the yellow light goes dark, a working position has been found.
Next, I ordered a blank key online for 20 € including shipping. At a nearby locksmith I got the milling done, that cost 26 €. The total costs amount 46 €. I think that is still somewhat costy, but at least not as steep as the regular options mentioned above.
Here is a short video demonstrating starting the engine with the transponder taped to the car. The keys don’t need to have any transponders anymore. Notice the indication light of the engine immobilizer.