Most lifeforms can hear sound. Most use this as a warning mechanism. What if we incorporated it into UFOai?
Here's how it would work: Each action has a "noise" factor, ranging from low(tiptoe) to high(gunshot). Actors can do some actions more or less noisily based on their weight, mind, and movement. Noise is also affected by the distance between the source and any listeners, and also by certain items. Each actor also has a "hearing" factor, which is a level of noise above which the actor notices something fishy is going on. This level can be affected by remaining TUs(how fatigued someone is), mind, and a new trait, "sensor input"(how well someone hears/sees). Noises heard by a friendly actor are marked onscreen with a symbol until the source of the noise is discovered.