This is an unofficial NeoForge 1.21.1 port and I am not the owner of the mod.

You can find the original mod here (for Forge 1.20.1 and below) or here (for Fabric 1.20.4 and below).
What's in the mod?
Online Detector is a mod that was made to help manage machinery - such as Create Mod, Mekanism, etc. - and/or redstone contraptions on servers. The mod adds two new blocks called Online Detector and Advanced Online Detector. The first always tracks the owner (the player that placed the block), while the second comes with a GUI to choose the player it should track. The Online Detector blocks output a redstone signal while the tracked/bound player is online.
Who made the mod?
The original Online Detector was made by the wonderful andrew0030. All credit for the idea, the original implementation, and all artwork in and outside the game goes to them (and their team, such as it is).
The only original work I did was to use AI as a tool to port the mod from Forge 1.20.1 to NeoForge 1.21.1, while andrew0030 is busy with his other wonderful projects. I used ChatGPT Astra 6 Medium on a premium tier subscription. The mod was tested by real players. It was developed on Minecraft 1.21.1, Java 21, and NeoForge 21.1.248.
Please go and give the original author (again: andrew0030) your love and support their work!