Modules act as a major element of strategy in the game as they extend the player's longevity and greatly aid resource generation. They are at least as important as the player's Heroes - smart placement, research, and budgeting of modules can win a game as easily as the inverse can ruin one. Placing modules requires an appropriate module slot in a powered room and an amount of Industry. Modules can be placed at will if these conditions are met, and any placed module can be destroyed by the player at will using the bulldozer button on the bottom of the UI (though spent Industry is not refunded). Players can also upgrade modules and their effects by spending Science at an Artifact.
Modules all have health and defense values just like heroes and can likewise come under attack by certain monsters. Heroes with the Repair skill are able to automatically heal a module for no cost by simply standing in the same room. This happens much slower while monsters are alive on the floor, making it difficult to actively tank modules in combat. Similarly, modules placed while monsters are alive on the floor also build much slower, encouraging the player to build in advance as a result.
Major Modules are structures that may only be built on a major slot. A major slot is a large, central slot shown as a plus sign. There are either 0 or 1 of these slots in each room. Steles, Artifacts, Dust Factories, and Cryo Capsules all spawn on a major slot, and anything but Steles can be razed. After a Major Module is built on this slot, it services the entire floor, not just the room it is in. These Modules specialize in Food, Industry, Dust and Science(FIDS) output or stat boosts.
The Food Replicator, Industry Generator, Science Creator, and Emergency Generator modules all have incremental industry costs, which increase for every major module on the floor. All other modules have flat costs. Heroes with the Operate skill and Mechanical Pals can vastly increase the performance of a major module in the same room. Major Modules vary in their HP and defense, with higher levels adding more durability.
Minor Modules are modules that may only be built on the smaller, minor slots. There are 0-8 of these slots in every room. Once built, a minor module will only influence the room where it was constructed. These modules are still extremely valuable however and have a range of uses, mostly focusing on attacking monsters, buffing heroes, or providing economic benefits. Minor Modules also vary in their HP, with higher levels adding more durability, though the defense value of all minor modules regardless of level is 15.