Activate a buzzer when power goes off
The simplest circuit would be a 220V relay and a 3-4.5V buzzer. Connect the battery and buzzer to the N.C. (normally closed) and COM (common) connections of the relay, and connect the relay coil to 220V. The 220V will hold the relay open, and when the electricity goes off the NC and COM connections will be connected internally, powering the buzzer.