Aliens

They could have a communication system based on entanglement. They could have wormholes to a central comms hub.

My rummaging on arXiv hasn't yielded any feasible approaches for FTL communication based on quantum entanglement so far, since a classical (information) channel (limited by c) has been required for all of them. If an alien civilization has access to wormhole technology, it would (if I recall correctly) require considerably less energy per bit of sent information to use microwaves than to use entangled particles.

Thus, unless the alien civilization goes out of its way to remain invisible in the EM spectrum, or perhaps unless it needs to transmit information through a planet, it will probably be more likely to use microwave communication that we can detect. Unless they've limited themselves to masers...