We should have a new tower called a
Surveillance Tower. When placed, it would give a player message alerts in the corner when units that are un friendly are coming. This building would require a
Surveillance Center. As for the price of these towers, I was thinking we could have two. A short range and a long range
Surveillance Tower. The short range ones would be cheap but they can't 'see' far thus not alerting you to intruders until they are quite close. The long range one would cost more but give you a waning with plenty of time to prepare. The main use of this tower would be to warning you of raiders and sneak attacks.
Here's an animation. My idea was to have a satellite on top of a tower. Sorry, im not the best drawer

When the satellite is facing away from you, thats the worse part of the animation. But you get the idea.
