iOS 12
Flash the LED for alerts on iPod touch
If you can’t hear the sounds that announce incoming calls and other alerts, iPod touch can flash its LED (next to the camera lens on the back of iPod touch). The LED flashes only if iPod touch is locked.
Tip: LED Flash for Alerts is a useful feature for anyone who might miss the tones associated with calls and other alerts in a noisy environment.
Go to Settings
> General > Accessibility > LED Flash for Alerts, then turn on LED Flash for Alerts.To prevent LED flashes when iPod touch is in silent mode, turn off Flash on Silent.