What makes a good 'radio scanner' for listening to police bands?

[p0ntif]

I am looking for a piece of equipment like a 'police scanner' or a 'scanning radio'. I know very little about these things, and don't know what to look for! Please enlighten me! What makes these things good? Or rather what makes one type better than another? Will one from the 70's work just as well as a current brand new model? Any benefits or caveats to any of these things?
share your knowledge and experiences!

thanks!

 

[Descartes]

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