the so called "smart lock" is really a horrible experience.
firstly, the host said after registration, the app nuki would automatically generate an email to me, however me and my family members didnt receive any email just few hours before check-in. i asked the host to check, he promised he will check, but finally no feedback until passed the check-in time. no reply from the host, I walked around and stayed in my friend's house. finally i got the message from the host, he said the email had been sent a day before, so what did he really check few hours ago?
worse still, i arrived the house at night, and the code didnt work! my whole family was standing in front of the door, freezing. luckily, the host got a helper next door, who is a very very helpful one, she came and fixed the "smart lock".