Usually it's just a spy plane. Sometimes from the same country. Or a weather balloon, falling satellite, or just instrument errors. It's never been aliens. And if aliens can get all the way here, they aren't doing some shifty shit like being detected by friggin RADAR! Can you imagine how embarrassing that'd be?

"Hey Quizlock, we heard you did some recon of Earth and the humans caught you on their radio frequency detection and ranging devices! How'd you manage that? Blast visual data at them and not absorb anomalous spectra? What an amateur! Now get back to reconfiguring the new quasar drives!"