"This spread has a transparent object"

[MarieMeyer]

In the Pages panel, I am seeing an icon alerting me to the fact that "This spread has a transparent object". How do I find that transparent object so I can investigate it?

[Steve Werner · Accepted solution]

Choose the Window menu > Output > Flattener Preview. In InDesign go to the spread where you see the transparency icon  in the Pages panel. In the Highlight menu, choose Transparent Objects. If you go to a new spread, click the Refresh button.

[rob day]

You can also use preflight to check for transparency—the Preflight panel will give you a clickable list of objects with any transparency: