You noticed the thumb button in the center of the device.
Here are the steps to follow to determine the type of ballast in your light fixture:
You won't need a ladder to 'read' the fixtures.
Just point and 'press'
If the light on the device shows "Red", a Magnetic Ballast (old-style technology) has been detected.
Should the light show "Green", this means that electronic ballasts are operating in the fixture.