It sounds like your that model's emergency button is only used to lock video file? not a G-sensor trigger button?
Nearnly all of car dvr works like this,when we set up G-sensor to be on,when car dvr detects any crash,it will be able to protect the video file of "the after and before event such as 10Seconds around(For example"
The faulty button still does not affect your normal use of emgency video function.
Maybe you had better not return the camera back to seller first,you do a test by start recording videos, then knock car dvr heavily and see if the car dvr can have a lock icon or not (Or if it can lock any video files when we playback all video files and find out the files in emergency files)If it exisits any of above mentioned situation,then car dvr should be used normally.
Wish you good luck
Kind regards,
joovuu.com