Doorbell

It was just past eleven on a Tuesday night in a mid-rise Hangzhou apartment block when Wang Lina’s phone buzzed to a thumbnail of a delivery rider. Rather than pad to the door, she opened the Mijia app, used the lock’s voice-changing intercom, and told the rider to leave the box in the building locker — a nine-second transaction that is the entire value proposition of the new Xiaomi Smart Door Lock 5C Cat’s Eye Edition, on pre-sale at ¥999.