You could hook into the buzzer circuit for this notification.
So where possible, I shy away from any modifications to the device itself that aren't extremely simple to undo.
A vibration sensor and hall sensor on an esp8266 is cheap, works consistently, and is VERY easy to take off if I don't want it any more.
I did hook into a humidifier once kind of like this, I hooked the esp8266 up to the on-off button, but I try to avoid it if I can.
You could hook into the buzzer circuit for this notification.