Door be locked, or not? / Door be locked, or not?

Every time, when in the toilet or bathroom, were repeated to check carefully the door quickly, or nervous after use, Now you can use the cleverer way,For example: The users and the outside ones can be ' very clear ', OK?
Seemingly ordinary door knobs into the actual door knobs What's the difference? When you use, press the lock, the door and the door will show warning light, not only to remind users can also allow outsiders to know, not reckless intrusion.
Certainly, pushing the lock can reach the same result too. But, don’t you think let use such a door knob will feel comfortable when using space, isn’t it much “Smart”?