When one key still works
Keep it available and describe what it does. Does it start the car, operate the remote buttons and open the door with a blade? If one part is damaged, explain that too. A split plastic case and a failure of electronic recognition aren't automatically the same fault.
Say what you want from the spare. Another fully usable everyday key and a limited backup may be different requests. The vehicle and intended functions should determine what is proposed, rather than the appearance of a replacement case.
When there is nothing left to start it
Tell the locksmith that all keys are lost. Have the year, make, model and vehicle location ready. A replacement without the original can be possible for some vehicles, but parts and the required electronic work need checking for the actual setup.
Don't assume the only next step is a tow, and don't assume that a locksmith can handle every vehicle either. Compare the available options after checking what each can supply. Permission to work on the car must also be established.
The part, the cut and the recognition
A key bought online can look right while being unsuitable. Ask about the specific part before buying it. Keep the seller's listing and packaging if it is already purchased, and say whether it is new or previously used.
A price for cutting a blade may not include making the car recognize the key. A quote for electronic work may not include the replacement part. Remote buttons can add another function to clarify. Compare the same finished key rather than only the lowest number.
Test it, then keep the spare separate
Try the functions included in the work on the actual vehicle. If a mechanical emergency blade is supplied, check it without closing yourself out. Keep another working key nearby during testing when there is one.
For a Sun City parking-area request, name the lot, entrance and vehicle position. A center or shop name may not identify the car. Once the job is complete, store the spare away from the everyday key ring; two keys carried together can still be lost together.