[norea-armozel]

The physics of electromagentism doesn't diverge all that much when you're talking about stray signals from alien satellites or radio arrays. So long as you use the radio spectrum to send signals out to satellites or interplanetary systems (probes, colonies, whatever) you're going to get spotted. Laser signaling may be the only alternative I can think of that wouldn't be so easily detected and probably lower power too, but that's it.

The only other alternative I can hazard speculation on is possibly gravity wave signaling? It's a bit of a stretch in my mind since the only real way to do that is to assume certain kinds of unproven particles like gravitinos (these are supposedly able to be interacted with in superconducting materials last time I read about them).