Huawei
Set a Mobile Data Usage Warning auf Huawei
EMUI tracks mobile data usage on the device itself, separate from what your carrier reports. This on-device counter is what triggers the usage reminder, so the notification appears based on the phone's own measurement rather than a live carrier feed.
To turn it on, open Open the settings ➔ Tap on Mobile network ➔ Tap on Data usage ➔ Tap on More data settings ➔ Tap on Usage reminders. From there, Push the bar to the left or right to set a limit and a reminder, which lets you pick both a maximum data limit and the percentage at which you get warned.
A daily reminder works the same way but resets every 24 hours, which is useful if you tend to binge-watch or download large files on specific days rather than steadily through the month.
If you go over the limit anyway, EMUI lets you choose whether mobile data simply gets disabled or keeps running. Since the counter is device-side, expect small deviations from your carrier's own billing numbers, especially right after a plan reset.
If you need hard enforcement instead of a warning, look at the data limit option in the same menu instead of relying on the reminder alone.