If I attack with the Fathomless’ tentacles on a creature that is unaware of where I am, will it become aware of my warlock?

Have been playing a Fathomless Warlock recently, and have found the way the tentacles function outside of attacking and moving it is somewhat vague. If I use the tentacle to attack someone who doesn’t know I’m there, will they become aware of my warlock? I assume this is up to the DM but my DM wanted to try and reach out first.