I came from another reputable smart door lock that drained my iPhone battery like crazy when using the geofence to allow the smart lock to open upon arrival. So, the U400 saved my life… my wife would have disappeared me if I didn’t answer her call. A dead phone was unacceptable. Now, my battery never dies, but I have to talk to my wife longer, or she will disappear me. 
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Btw, if you have an Apple Home key (and selected the “express mode”, the one that doesn’t need Face ID to unlock the door), you will be able to unlock the door via iPhone even if it’s dead.
When it’s dead then it won’t utilize UWB (just NFC), but it’s still a cool feature as you don’t need to race to your door when your phone’s at 1% 
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Great you have such a good experience with the U400 
I already wait for that feature on a European smartlock from
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