Background Art Generally, a door is used as means for coming in and out from a confined room, and a door lock is mounted on the door to unlock and lock the door.

In case of a door lock, various measures have been developed, which easily lock a door or make it impossible for a stranger to unlock the locked door without keys.

And, to notify the coming in and out through the door, the stranger should knock the door or push a doorbell installed on the door.

However, for the above method of noticing the stranger's coming in and out through the door, there has been raised a problem in that the stranger could be noticed only when he or she knocks the door or pushes the doorbell. In other words, when the stranger opens and shuts the door slowly in order not to let a person (or dweller) inside or outside a room know his or her entering through the door, the person can hardly sense it, which makes it impossible for the person to check the invasion of the stranger. Also, it is quit noisy to notify a passenger's coming in through the door by knocking the door, opening and closing the door while making some sound or pushing the doorbell.

Moreover, in terms of carefulness in use, the passenger feels inconvenient.

Disclosure of Invention It is an object of the present invention to provide a door lock that more conveniently notifies a stranger's coming in and out through the door by alarming when the stranger rotates a doorknob of the door.

To achieve above object, as embodied and broadly described herein, the present invention provides a door lock including: a rotating axis installed on the inner space defined by fixing plate and a doorknob fixing cover for fixing a doorknob to a door, and having a toothed wheel consisting of a plurality of protrusions protruded from the circumferential surface of the front end thereof; an actuating bar rotatably mounted on one side of the fixing plate by means of a hinge in response to an elastic force of a spring, and having the lower end portion of which is mesh-engaged with the protrusions of the rotating axis of the doorknob; a striking member fixed to the front end of the actuating bar and going forward and backward according to the movements of the actuating bar; and a sounding plate having one side fixed to the doorknob fixing cover and the other side in contact with the striking member of the actuating bar, whereby making a sound in response to a rotation of the rotating axis of the doorknob.

That is, the door lock is structured in such a manner that the rotating axis of the doorknob is consisted of the protrusions, configured like a toothed wheel, and on the fixing plate is rotatably mounted the actuating bar, the lower end portion of which is mesh-engaged with the protrusions, by means of the hinge. According to the above structure, the striking member of the actuating bar strikes the sounding plate when the striking member is rotated by the rotating axis of the doorknob, which in turn generates the sound when the striking member and the sounding plate are in contact with each other, thereby notifying the stranger's coming in and out through the door.

Brief Description of the Drawings FIG. 1 is a schematic view illustrating the state of a door lock and enlarged view of the principal parts of the door lock according to the present invention; and FIG. 2 is a view illustrating the operational state of the door lock according to the present invention.

Best mode for Carrying Out the Invention Now, an explanation of the preferred embodiment of the present invention will be in detail given hereinafter with reference to the accompanying drawings.

Referring to FIGS. 1 and 2, a door lock 2 is configured to generate a sound when a doorknob 3 of a door 1 is rotated. The door lock 2 includes: a rotating axis 4 installed on the inner space defined by a fixing plate 6 and a doorknob fixing cover 11 for fixing the doorknob 3 on the door 1, and having a toothed wheel consisting of a plurality of protrusions 5 protruded from the circumferential surface of the front end thereof ; an actuating bar 7 rotatably mounted on one side of the fixing plate 6 by means of a hinge 8 in response to an elastic force of a spring 10, and having the lower end portion of which is mesh-engaged with the protrusions 5 of the rotating axis 4 of the doorknob; a striking member 9 fixed to the front end the actuating bar 7 and going forward and backward according to the movements of the actuating bar 7; and a sounding plate 12 having one side fixed to the doorknob fixing cover and the other side in contact with the striking member 9 of the actuating bar 7, whereby making a sound in response to a rotation of the rotating axis 4 of the doorknob.

That is, the door lock 2 is operated in such a manner that when a stranger rotates the doorknob 3, the rotating axis 4 of the doorknob 3 is rotated while the protrusions 5

touches the lower end portion of the actuating bar that is mesh-engaged with the protrusions 5, and accordingly the actuating bar 7 is rotated about the hinge 8 while bearing up against the elastic force of the spring 10. At this moment, the lower end portion of the actuating bar 7 is released from the protrusions 5 and returned to its original position owing to the elastic force of the spring 10, which will in turn makes the striking member 9 that is disposed on the upper end portion of the actuating bar 7 strike the sounding plate 12 installed on the doorknob fixing cover 11, thereby making the sound.

Accordingly, when the stranger rotates the doorknob 3 in order to open the door 1 closed, the plurality of protrusions 5 formed on the rotating axis 4 of the doorknob pass beneath the actuating bar 7 while touching it, and accordingly, the striking member 9 of the actuating bar 7 strikes the sounding plate 12 several times, thereby notifying the stranger's coming in and out through the door.

Also, in the case where the door lock 2 is installed on the doorknobs 3 protruded from the front and rear sides of the door 1, respectively, the sounding plate 12 sounds an alarm when the stranger comes in and out from a room, so that both the stranger's coming in and out can be noticed. And when the door lock 2 is installed on either the inside or outside of the door 1, either the stranger's coming in or out from the room can be noticed.

Furthermore, in another embodiment of the door lock 2, an electronically operated sound-generating unit can be substituted for the sounding plate 12 installed inside the doorknob fixing cover. So, when the striking member 9 of the actuating bar 7 turns on a switch of the sound-generating unit, the sound-generating unit sounds an alarm anytime the doorknob 3 is rotated, thereby notifying the stranger's coming in and

out through the door.

Industrial applicability As set forth in the foregoing, a door lock according to the present invention has advantage in that when a stranger rotates a doorknob of a door to open the door, a sound is generated, so that the stranger's coming in and out through the door can be easily and simply noticed without a need of installing a separate doorbell, thereby providing convenience in use.

Although the invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.