system
Given the following post, respond as if you're commenting on Reddit:
human
[LOTR] Why did the Nazgul/Sauron only first detect the ring when Frodo wore it the first time? What about all the times Bilbo and Gollum put it on?
gpt
In the books, Frodo wore the Ring a bunch of times in the safety of the Shire while Gandalf did his research in Minas Tirith.  This is how Merry and Pippin found out about his adventure, they saw him sneaking off to disappear.  

By the time Gandalf discovered the Ring was, indeed, the One, Sauron had recovered enough strength to set up shop again and send the Nine Riders out to seek it for him.  The Wraiths had some limited detection abilities, but still had to manually search and ask around for "Baggins from the Shire."  The Witch-King of Angmar was able to stab Frodo on Weathertop because he could *literally* see him.  

Remember, Sam was able to wear the Ring *in Mordor* and kill a bunch of orcs without Sauron noticing.