Not a gaurantee. Literally my first time through security after I got PreCheck, I was randomly beeped by the metal dectector and told I could either go through the scanner or opt-out and get a pat down instead. I opted out, like I've always done and got yet another pat down. Since then, I've had the metal dectector randomly beep a second time but was only asked to swab my hands to check for explosives.