Not sure if this apples to all "smart keys" but I owned a Volvo S90-T6 sedan with one of those keys---it was required to start the engine as well as trigger the alarm and PDL's
I wanted an extra key allowing manual door lock operation so that once started (with the "smart" key) I could warm the interior before driving. I had to buy the key from the dealer who required me to bring the vehicle registration for the VIN, keys were specific and already cut to the VIN.
The "smart" key did allow me to lock and unlock the doors with the engine running so I saved myself well over $100 avoiding that new key being flashed so it too would start the car.
Keep in mind this was on a 1999 Volvo so another year and make may not work the same way---investigate this as an option for your particular vehicle.
I have several dumb door lock keys for each of my vehicles. They come in very handy when you get locked out while camping.
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Current van: 2002 Ford E350 extended body camper with Colorado Camper Van pop top and Agile Offroad 4WD conversion.