Should be 99% Invisible.

And there is plenty of us! But ... where are you?

Most SETI projects are focused on listening for transmissions in the relatively quiet slice of the radio spectrum between the radio spikes of hydrogen and hydroxyl, sometimes called the Water Hole. These would be messages deliberately sent, delivered to a sort of cosmic mailbox for us to read. It doesn't matter that the senders might no longer use radio to communicate amongst themselves. The messages are meant for us.