Decide what the spare needs to do.
Opening a door, starting the vehicle and using remote buttons are separate functions on many cars. A low-cost mechanical backup might solve one problem while leaving the others untouched. Name the functions you want before comparing options.
Keep the working key available.
An existing working key is useful for identification and may affect the procedure. Keep every authorized key available in case the vehicle-specific process requires them. Do not assume a replacement will automatically preserve every existing credential.
Test the result in ordinary use.
After the agreed work, check the intended functions: the blade, door controls, remote buttons and starting as applicable. Store the spare separately from your everyday key in a place accessible only to authorized people.
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