Even with 3 PER you can out-stealth and out-spot enemies.
1. Detection improves with levels.
2. Detection Goggles.
3. Paranoia*
4. Min 6 AGI and max Stealth with bonus Stealth gear.
5. Move slowly.
6. Some meta-game knowledge or just common sense - you are in Lurker or Lunatic area.. or "It's too quiet." 🤨
Also, if you CAN'T out-spot, Quick-Tinker and get to a corner.
Also, also - if you know that area is nasy, place Bear Traps in a choke-point (make sure no other way to you exists) and detonate a Frag or HE grenade or TNT behind you and wait around a corner or some place out of sight of those Bear Traps. Once you hear them snap, start combat manually, show yourself to those trapped and have fun. Any stealthed enemies still coming in, will be in combat, so you can flush them out with more grenades and/or Flares 😁. BTW, if there is no other way to you, even 0 Trap skill Bear Traps will work 😄