There are three different Amazon devices that use echo: the original echo cylinder, the echo remote, And the Amazon fire TV remote. Only the first is completely hands-free. But if you were considering the echo remote (which requires pushing a button while you’re talking) then the fire TV voice remote might also work well.
If you’re asking about a completely different voice method, there are many. Anything which can send a voice text to IFT TT can be used to trigger harmony or smartthings through their IFTTT channels.
The following thread discusses various voice options: