Wouldn't you love to know where that police helicopter is going in such a hurry? 
Wouldn't you like to know what all those sirens are for approaching your neighborhood? 

What is a trunking scanner?
This is an often asked question... On a normal old fashioned scanner (non-trunked) we used one channel (or frequency) for each police dept channel, or in the old old days we had one crystal for each channel... Now since the frequency ranges the cops use are becoming more crowded many depts are going to computer controlled channel sharing.. this is called trunking... now with trunked radios the cops can get many many channels on just a few frequencies and the computer that runs their trunking system will choose a clear frequency every time a cop keys his radio..!!  This could mean that every time a cop keys his radio he might be on a different frequency, but to him is seems like one simple channel....    for us listeners it makes it hard to listen since they might be on a different frequency every time they talk..!!  Now we have TRUNKTRACKER SCANNERS!!  AHA!
Makes it simple for us again....     Most of the 800Mhz police are using trunked radios!! But there are still many departments out there that use the old fashioned non-trunked radios!