ZTE Nubia Z9 hard reset
You can reset your ZTE device's password after power on: input *983*987# in emergency dial-up pad. Select Erase everything. It will restore factory settings and your personal data will be erased.
You can access to emergency dial up even the phone screen lock is on.
Another way to reset your password or gesture lock on your ZTE Nubia Z9 is
ZTE Nubia Z9 Andorid recovery menu
Turn off your device. (Sometimes you have to remove the battery and reinsert it before this procedure, if the device has a removable battery.)
Press Volume UP + POWER ON the device.
Keep pressing both key until the Android recovery menu appear.
Now select from the following options.
Highlight wipe data/factory reset with Volume key (power to confirm).
Now highlight Yes -- delete all data and press power to confirm.
After done select reboot system now.
All data will be deleted!
ZTE Nubia Z9 hard reset from menu
Or if your phone is responding to screen input, then open Settings from the Applications menu. Tap Backup & reset > Factory data reset, click Reset phone and then Erase everything to format your phone.
To reset the ZTE Nubia Z9 device from time to time for optimum performance, power off the device and remove the battery. Reinsert it and turn on your Andorid phone.