The Sunblinkers

Imagine you want to get the attention of intelligent beings in stars that are light years away and you don't want to build giant lasers or radio emitters. Instead, you choose to use the already available power of the sun and modulate its reflection to give you all the power you need. They started small with Solar Updraft Towers off the coast of Africa to bring rain to the Sahara. They had already purchased as much of the land around the ancient river systems as their funds allowed and when this region began to live again, they sold it all for thousands of times their initial investment.

Next, they purchased the latest and greatest 3D printing setup with its thousands of tentacles and started harvesting all of the debris in orbit that wasn't actively being claimed and paid for. They cloned the initial ship into enough to complete the process in less than 90 days. They then took their fleet of processors and started converting the asteroid belt into mirrors. The mirrors had a cooling system that generated power by using the differential of the heat and the cold of space.

Earth now had access to cheap, reliable power to push people or cargo anywhere they wanted. What no one realized for the first decade was that the Sunblinkers were living up to their name. They had built coating on all of their mirrors that could be switched from fully transparent to zero transparent in a femtosecond. They had been sending simple messages to every star possible the entire time they had been operating. Once Alpha Centauri started responding, we figured it our fairly quickly.

We are now in contact with two different races of beings and the news from both was to stop sending messages and start preparing for battle. We are not alone and most are friendly but the bad ones are planet-destroying sort. This gives the Drake Equation a new wrinkle.