I am 100% for PreCheck at SEA (knock knock) and have never had any issue with the metal detector. I do always have to take my shoes off because I wear heels every day and they all have metal in them, but they never make me remove anything else - not even my long leather coat that I wear most travel days in the cooler seasons.

Even if I'm traveling out of the N gates, I still use that lane because I can grab a decent coffee at Dilettante and then head to my gate.