after watching this video, I would not trust any z-wave device for security related functions:
https://www.youtube.com/watch?v=gn-amPvXn6M
that is a problem of a closed protocol and very bad implementations
from hardware vendors.
Hacking Z-Wave Home Automation Systems
Re: Hacking Z-Wave Home Automation Systems
Pity for you 
In fact, Z-Wave protocol is secure and many people inspected it and found no problems in the design. And this is even stated in this video.
As for implementation in specific devices, it is not related to close protocols. How often you find bugs in Linux kernel, OpenSSL, Firefox, .... Pretty often! And all these are open source projects!
Do not mix Z-Wave design and specific devices - having good protocol does not make all devices secure.
By the way, same is applicable to other protocols (including SSL - OpenSSL is a good example!)
In fact, Z-Wave protocol is secure and many people inspected it and found no problems in the design. And this is even stated in this video.
As for implementation in specific devices, it is not related to close protocols. How often you find bugs in Linux kernel, OpenSSL, Firefox, .... Pretty often! And all these are open source projects!
Do not mix Z-Wave design and specific devices - having good protocol does not make all devices secure.
By the way, same is applicable to other protocols (including SSL - OpenSSL is a good example!)