How would I set up an entity to fire outputs based on line of sight?

[Moffein]

I'm currently working on a CS:GO map, and I would like to add moving guards that fire outputs when they see players that aren't hiding behind cover. I'm planning on setting up the guards themselves using a func_tracktrain, func_breakable, and prop_dynamic, but I'm not sure how I would go about with allowing them up to "see" players. Is there any way to achieve this effect using either entities or vscripts?