1. I'm not aware of any smart lock that cannot be locked and unlocked manually from the inside. This would violate fire code for residential structures in a lot of US jurisdictions.
2. Electronic locks in general are either line-powered or battery-powered. Line-powered locks are unusual in residential environments because of the higher complexity of installation (they're more often strikeplates than actuators, although in-door actuators are available).
Battery-powered locks take one of two approaches to resolving power issues: most commonly on residential locks, there is still a key cylinder on the outside to manually lock and unlock. Less commonly on residential locks but more typical of commercial ones, there may be no key cylinder but instead an external connector that allows the programming tool (very common on commercial systems) or a 9v battery (common on residential units) to be connected to provide external power.
3. Cloud-reliant smart locks are pretty rare for practical reasons. Most are still fully functional (often minus remote control via app, but not always) without internet service. Even most commercial systems fall back to cached credentials in the door controller when the connection to the access server is lost, although annoyingly some of the newer "smarter" systems don't.
I have the Nest/Yale lock without the key, it definitively is not reliant on the Nest cloud being up (or internet working) for access, only to remotely lock/unlock or to program new codes. Do any locks actually fail to work with an already programmed PIN code if the internet is out? That seems like a massive failure. Go to dinner and your router crashes and you can't get back inside to fix it? Wow.
The only examples I know of are commercial systems, and specifically "cutting edge" commercial systems that are completely IP-based and cloud-managed. These are honestly kind of a disaster and I hope they don't catch on; they can be cheaper to install than conventional commercial systems (with ACU cabinets) but they achieve that cheapness by abandoning most of the reliability and security features of conventional designs. That said some of these get installed fail-open (e.g. loss of management means they stay unlocked) for fire egress reasons.
1. I'm not aware of any smart lock that cannot be locked and unlocked manually from the inside. This would violate fire code for residential structures in a lot of US jurisdictions.
2. Electronic locks in general are either line-powered or battery-powered. Line-powered locks are unusual in residential environments because of the higher complexity of installation (they're more often strikeplates than actuators, although in-door actuators are available).
Battery-powered locks take one of two approaches to resolving power issues: most commonly on residential locks, there is still a key cylinder on the outside to manually lock and unlock. Less commonly on residential locks but more typical of commercial ones, there may be no key cylinder but instead an external connector that allows the programming tool (very common on commercial systems) or a 9v battery (common on residential units) to be connected to provide external power.
3. Cloud-reliant smart locks are pretty rare for practical reasons. Most are still fully functional (often minus remote control via app, but not always) without internet service. Even most commercial systems fall back to cached credentials in the door controller when the connection to the access server is lost, although annoyingly some of the newer "smarter" systems don't.