Here is an indoor siren that combines with your Netatmo indoor camera to alert you when an intruder is detected. The Netatmo Smart Indoor Siren has a 110dB alarm. It comes with auto arm and disarm functionality. It can also play pre-recorded noises to make it sound like you are home when you are not.
The Netatmo Smart Indoor Siren relies on the camera’s facial recognition to go off with no false alarms. You can find out more about it here.