I don't think they really mean backup frequencies, more backup transmitters. They are licensed for a very specific set of frequencies and the Friendly Candy Company in Washington DC gets cranky when you start using someone else's frequency. They do have some backup non-trunked talkaround frequencies available to them as a failsafe mode, but I don't think things are that bad yet....Mine are back up now. Lots of static but readable. I was getting nothing until about 10 minutes ago. If these are the back up freqs, why can I hear them when they are not entered into my scanner?