With every new Genshin Impact update, we get new characters in the game, and to ascend them, we need to farm their ascension materials. One of them is the Subdetection Unit which is an ascension material required to ascend characters like Wriothesley, and it will become available in Genshin Impact 4.1 update to farm.
As per its in-game description, these are "Detection units produced by Fontaine Research Institute using new models of artificed components. Its original purpose was monitoring all kinds of environmental data." Since Fontaine will be expanding with the new update, you will be able to find Subdetection Unit in the new areas; however, it will be a difficult task to explore a massive region to farm them, and thus, here are their exact locations to save you a lot of time.
Genshin Impact: Subdetection Unit Farming Location
Subdetection Unit is a local speciality of the Fontaine and can be found in abundance in the Fontaine Research Institute of Kinetic Energy Engineering Region. You can have a look at their location marked on the map below:
You will need a total of 168 Subdetection Units to ascend Wriothesley to his highest level, and as per the speculations, you can farm around 64 of them in a single run. After that, you will have to wait for them to respawn to grab the next batch.
You can travel fast from one location to another by using Teleport Waypoints and the Statue of Seven to collect them quickly. In addition to this, make sure that your HP is enough to fight enemies, as you might encounter some while exploring.