With the rear cover removed, we get our first look at the photoplethysmogram (PPG) heart rate sensor.

A PPG is generated by shining light onto your skin and measuring the reflected light, tracking blood flow and therefore your pulse.

There are several markings as well:

FCC ID: IHDT6QC1

Anatel ID: 1510-14-0711

Anatel is a Brazilian government telecommunications agency that approves devices for marketing and sale in Brazil.