Deep Space Settlement is a 4X real-time strategy game focused on empire building and grand-scale space battle.
Each ship emits and reflects infrared and light radiation. Sensors for each categories can be built to detected those ships.
Reflection is based on the albedo of a ship's surface and the nearby star that emits all kind of radiations. Higher the albedo, higher the reflection and susceptibility of being detected.
The ships will also emit radiation when firing weapons, increasing the probability to be detected furthermore.
And finally, some engines and reactors emit a lot of radiation, like the anti-mater reactor. These aren't for stealth missions to say the least.
There are also x-ray and gamma ray sensors but those are for more specific uses like detecting ships in dust clouds and detecting warp in/out.