For Mc...: Invisible Players Detector Resource Pack

: A lightweight pack that replaces subtle particles with bold, high-contrast warnings designed for fast-paced combat.

: Uses core shaders to uniquely change only invisibility particles to a bright yellow color without affecting other potion effects. INVISIBLE PLAYERS DETECTOR RESOURCE PACK FOR MC...

: Modifies invisibility particles to be bright yellow and changes other potion effects to different colors for easy identification. : A lightweight pack that replaces subtle particles

nothing on the ground and nothing next to the doors. either. so let's just approach them and see if we can investigate. something. YouTube·NiclasBlocko's Minecraft nothing on the ground and nothing next to the doors

: Replaces potion particles with a red "caution" mark and can add a "Steve marker" indicator above players' heads for exact positioning. Non-Pack Detection Methods

If you don't want to use a resource pack, you can use these vanilla methods: Minecraft - Invisible Player Detector (Survival friendly!)