Basically we wanted a little bubble to appear to signify when enemies are aware of your presence.
Normally when you're out of range, the drone is in the Unaware state. You want to keep out of sight whenever possible.
When you get too close though, the drone enters the Suspicious state, where it will begin to look nearby for threats (you).
If you can manage to get out of range quickly enough, they'll return to Unaware and go about their business.
Different drones will react differently once they've seen you. Some will make a beeline towards you and others may call in reinforcements. It may be best to study their flight patterns and stay out of range or hide behind walls until the coast is clear. Since you have no way of destroying threats in TOC it'll be important to get a grasp on how to navigate with a certain amount of stealth.