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Re Die Hard, you didn't see Mc Clane retune the handset he was using..but he was transmitting on Ch9 - which was a designated emergency freq... and declared as such by him.
It is, within the CB band. But despite what you may have seen in media very few police agencies ever fit their cars with CB radios. Most of those that did were those that patrol interstate highways and similar, like CHP. The notion was that they would be able to hear accident reports, etc., from truckers. But their usefulness was found to be very limited (for a variety of reasons) and most of those CB radios were removed from police cars by the early 80s. And a police handheld cannot be simply "retuned" to work on CB, nor can the VHF or UHF handhelds in common use by security guards, etc.
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How well does it match the trope?