To provide a lock with an alarm device capable of detecting any illegal acts performed against a lock having an operating portion of a crescent lock, handle lock or latch installed to a window or door equipped to a window or door having a plate-shaped body such as a window or door; which is capable of detecting any illegal acts given to the lock of door or window and capable of generating an alarm without making error alarms.

In a crescent lock, handle lock or latch for a window or door in which an operating portion performing locking and unlocking operations is supported by a rotating member; the lock with an alarm is equipped with an abnormality detecting sensor detecting abnormal vibration or sound given to a window, door, window frame or door frame; an alarm mean for setting the lock to a stand-by mode until a predetermined time elapses based on an output signal from the abnormality detecting sensor and generating the alarm when an unlocking operation is performed through the operating portion during the alarm stand-by mode; and an malfunction operation preventing means capable of canceling the alarm stand-by mode of alarm means when it is set to the alarm stand-by mode by an malfunction.