They can also track who your devices are near. If your phone sits next to someone else's in an office building for nearly 8 hours a day and they know that persons job they can infer yours, especially since departments tend to sit together. Ad companies often assume recurring groups of people share overlapping interests (hence why their together multiple times) and will push out ads based on what other people around you are interested in to see if you are too.
They can also track who your devices are near. If your phone sits next to someone else's in an office building for nearly 8 hours a day and they know that persons job they can infer yours, especially since departments tend to sit together. Ad companies often assume recurring groups of people share overlapping interests (hence why their together multiple times) and will push out ads based on what other people around you are interested in to see if you are too.