this can be for a few reasons. Make sure they did not switch frequencies or that the police frequency is still programmed in. To make sure you know your local codes you can goto a website such as these two website 1, website 2,
where they may list the frequency needed. and last but most likely not the case is they do have private frequencies now that are encrypted with Motorola technology and requires a 8-16 digit passcode to hear the transmission. so if your trying to tune into a metro drug unit, or local swat this is the case most of the time.
If you need further assistance please feel free to follow up with a comment and i will be here to assist you. If this assisted you please feel free to rate the comment 4 thumbs up. thanks and
have a great day.