In Fahrenheit 451, when Montag visits Faber, Faber calls himself a coward. Why? In what way has he acted cowardly?

In their conversation, Faber tells Montag that, long ago, he noticed how the authorities (government, firemen, etc.) were beginning to become more oppressive. He says "I saw the way things were going, a long time back. I said nothing." Faber is a college professor. He is/was knowledgeable about dystopian narratives, the ways in which authorities can oppress and/or brainwash citizens, so he would have been able to recognize events shifting towards a more oppressive state....

In their conversation, Faber tells Montag that, long ago, he noticed how the authorities (government, firemen, etc.) were beginning to become more oppressive. He says "I saw the way things were going, a long time back. I said nothing." Faber is a college professor. He is/was knowledgeable about dystopian narratives, the ways in which authorities can oppress and/or brainwash citizens, so he would have been able to recognize events shifting towards a more oppressive state. Therefore, Faber (with this knowledge) felt he had a responsibility to speak out and protest this shift toward a more oppressive state where books are banned. Since he did nothing, Faber considers himself to be a coward. He adds that when books started being burned he "grunted" at first but no one would grunt (protest) with him, so he stopped. 

Faber has basically hidden in his home, hiding his open-minded thoughts in his own imagination. While secluded, he has developed the radio device that he will use to communicate with Montag. Again, he calls himself a coward for developing a device that will allow him to stay hidden in his home while someone else can go out into the world to secretly challenge the status quo. He tells Montag: 

Do you hate me for this electronic cowardice of mine? Here I am sending you out into the night, while I stay behind the lines with my damned ears listening for you to get your head chopped off.