I suppose you could have a look at EasyVR 3 Plus Shield for Arduino - COM-15453 - SparkFun Electronics for a voice recognition Arduino add on.
This can be programmed to recognise certain pass codes.
However, security systems which rely on voice normally work in another way.
A person registers, he repeats a number of training phrases, and his voice pattern is stored.
When the system requires the user to identify himself, he is asked to repeat a random phrase and the system can determine from the voice pattern if it is indeed the correct user.
For a voice operated lock, I could imagine that each possible user must register somehow ( maybe a wifi connected App etc.) so his voice print is stored and available to the lock. When the user requires entry, the lock voice module tells the user to speak a specific (random) pass phrase (or displays it on a display) and compares the result with the stored voice prints. A successful match means the lock opens.