Could aliens be using technology we cannot detect?

Yes — it’s plausible that extraterrestrial technology could exist in forms we can’t currently detect, but we don’t have any confirmed evidence that this is happening.

Why it’s plausible:

• Our searches have mainly focused on signals we know how to look for, especially electromagnetic signals like radio and optical emissions.
• Humanity has only been capable of sending and receiving electromagnetic signals for roughly 150 years, so our search window is still very limited.
• An advanced civilization could use methods that are hard for us to notice or interpret, or technologies that don’t produce obvious waste heat, radio leakage, or other familiar signs.
• Even if they did emit signals, those signals might be extremely weak, brief, highly compressed, encrypted, or otherwise look like ordinary noise to us.

A few caveats:

• Claims about neutrino or gravitational-wave communication are speculative; they’re physically discussed as possibilities, but not established as practical interstellar communication methods.
• Quantum entanglement does not let us send usable information faster than light, so it should not be treated as a known communication channel.

So the best answer is: yes, alien technology could in principle be undetectable to us with current methods, but that remains an open, speculative possibility rather than something we know to be true.