[quote=@Stern Algorithm]
<Snipped quote by DracoLunaris>

Sorry, not to keep layering you with "applying physics to sci-fantasy", but how would Stalker 'appear' under sonar/echolocation?
[/quote]

For simplicity, it works same as sight. After all, both tactically involve bouncing waves off of things. So living things experience what they think is there, and unliving machines freek out.