Smart fortwo Ignition Knob

I got this idea from an aluminum product sold in the UK. Yank your ignition key out of the key fob and stick it in this knob. It can now stay in the car, and most folks won't even realize the key is in the ignition. Most importantly, as Smart owners know, the remote is the immobilizer. Even if somebody were to try to start the car when you aren't around, it won't run. You can still lock the car, and basically forget the key even exists. Just unlock it, get in, and turn the knob. I set the tolerance based on my printer to be a semi-interference fit. No adhesive is required, there is enough friction to keep the key firmly in place. It's still removable with similar effort to removal from the factory key fob remote. If you want it made out of aluminum, here's a link to the UK product