Instagrammer Chris Ralph @chrisralphyq has posted up a snapshot of the new CheckMe O2 from Viatoma SpO2 monitor. This device can continuously monitor blood oxygen level and includes a BLE connection to sync the data through their iOS /  Android apps.  While there are many sub $20 SpO2 testers on Amazon the main benefits of continuous SpO2 would be for tracking sleep apnea, exercise performance/recovery and acclimatizing to a higher altitude.