ViATOM Bluetooth Pulse Oximeter Approved UK Built-in Offline Storage, Oxygen Monitor finger Adults for Heart Rate Blood Oxygen Saturation Includes Carrycase and Lanyard, Free APP
If your oxygen is lower or PR is lower/higher than the threshold, the WELLUE monitor will remind you with a buzzer and a corresponding readings flashing.
(Because wearing it for a long time will cause pressure on your fingers, it is not recommended to wear it overnight.)