(www.rboyapps.com - Making SmartThings Easy!)
You can check out the table in this post which compares locks features:
As far as keeping your existing key, that’s going to be an issue with any brand as they prefer their own keys. You could try rekeying it through a locksmith and see if they do it for different brands.
Without keypads in the US your best bet would be the August but you’ve ruled that out. You can check out the Yale and Schlage brands. I can say that deadbolt versions will have motor noise (Yale less the Schlage). If you don’t want motor noise look for the electronic latching versions from Yale and Schlage like the Schlage FE599, they’re very silent. As for Alexa, you will need either ZigBee for direct pairing or you will need to connect SmartThings to Alexa but you’ll have limited control of these locks through SmartThings for security reasons.
If the August was too loud for you, I think you’re out of luck with the list as you gave it. Every smart deadbolt lock has a motor that is physically moving the deadbolt. And those make noise, with the August being among the quieter ones.
There is an alternative as far as quiet goes which is to go with an electric strike instead. These don’t have a motor, they have an electromagnetic release for the door latch. They would be quiet and they can be made to work with voice assistants, but you aren’t going to be able to keep your existing key, because it won’t release the magnet.
If you’re interested in looking at the electric strike option, here’s a project report from one member who did that:
But unless @rboy knows of something, I don’t think you’re going to find smart lock that’s much quieter than the ones you’ve already tried.
Most lock manufacturers have been resistant to letting you unlock by voice.
You can sometimes get around this on some platforms, including smartthings, by having voice turn on a virtual switch and having the virtual switch separately trigger unlocking the door. Or use a real lightbulb if you don’t want to use a virtual switch.
Homekit will let me unlock by voice with my Apple Watch while I’m wearing it, but not with a phone or HomePod.
Alexa will let me lock but not unlock.
I understand their security concerns, but I still think this should be left up to the customer to decide.
I also understand the security concerns but it has been working flawlessly. You have to create a pin to allow unlocking. My frustration is that one day it just stopped working but the option is still there.