Apple
Go to Settings > General and tap About.
Look for the serial number. You might need to scroll down.
To paste this information, touch and hold the number to copy.
Samsung
Navigate to and open Settings, and then tap About phone or About tablet.
Google (Pixel)
Open your device’s Settings app.
Select About Phone or About Tablet.
Scroll down to find the model information or tap “Model” to view the device details. The serial number should be displayed there.