Perimeter alert to enemy transports

The best thing to do is to make a ship with a large sensor radius (if you have the Eyes of the Universe wonder, all of your ships will have large sensors). Send it to the space between your territory and theirs. Order the ship to "Guard". The sensor ship will then sit there inactive until it detects an enemy.

If any enemy ship comes in sensor range, the ship will be active on your next turn. So all you need to do is remember: if the picket ship is active, there is an enemy near.

Thanks, although a good change for DA would be for the ship to send a message that enemy ships are passing into out zone.

Pray you're not in the middle of the galaxy, then. I've had wars fought where the enemies were not even abutting each other because my empire was between them. The only way they could fight was travelling through my empire, which, given the level of development at the time this happened, would have amounted to some 20-30 alerts per turn from others entering my space...

It'd be nice if it were a toggle, but good god, lemme turn off the spam in the late game.

Another idea for DA or for Galciv 3 would be a sensor buoy. Instead of wasteing an entire ship just build some sensor buoys (maybe need a certain tech to build and there would be a small cost to produce but not as much as a ship)and tow them to your perimeter. When an enemy ship comes into range you would receive a message saying enemy activity had been detected by that bouy and the coresponding sector. Perhaps with higher techs and more credits the range and detail of information could be improved also they could perhaps be modified at high levels to be cloaked in some way so one could use them to spy on activities deep in enemy terrirotry or perhaps even specific planets. It would add another dimension to tactical plans of an attacker as the attacker might want to destroy or jam these buoys before sending there fleets into battle. Just a thought

Well, you can't tow ships in GC2.

You could just make a tiny hulled ship with sensors and no engines, weapons or defenses.
The basic hull has a speed of 1, so you could set its autopilot to where ever you want to place it. And such a ship would not cost very much.

I use a about 2-5% of my military resources per turn, building my sensor/intelligence gathering system. Basically the first part of it is a large utility hull ship, load it up with engines and one or two sensors, send it out to the perimeter of the empire, later in the game as the action starts to heat up, upgrade the design but keep the original design, build the first design with fast engines and out in the field upgrade them to the new design which is largely sensors, with few engines, that way as your empire size changes, you can use the forward deployed ships to change locations as needed, and only spend a minimal amount of resources to do so.

Other options would include keeping a defender or somethign in orbit around all your planets to avoid a transport invasion. Good smart sense.