To provide an alarm lock which effectively prevents an intruder from entering into a building through a window.

A body 2 of the alarm lock 1 is turnably fitted to a window frame 30 by the intermediary of a fitting part 3. A recess part 5 which is recessed to have a substantially U-letter shape is formed in a lower end surface of the body 2. By turning the body 2 downward to lock an operation lever 23 of a window lock 20 in a state that the operation lever 23 is housed in the recess part 5, the operation lever 23 is made not to be operable (not to be turnable). When the body 2 is forcibly turned upward, under the state of being locked, without pressing the pressing buttons 91 to 94 in a predetermined sequence, an alarm is generated through a speaker provided in the body 2.