In order to monitor them, you would need a scanner capable of trunk-tracking what's known as a Project 25 (digital) system. Some of the current models that will do that include: (handheld scanners) GRE's PSR-500; Radio Shack Pro-106 (essentially the same as the PSR-500, manufactured by GRE, but sold by Radio Shack; has a different front panel layout); Uniden BCD396XT. Base/mobile scanners (current models): GRE- PSR-600; Radio Shack Pro-197 (same basic scanner as the PSR-600, but sold through R/S stores); Uniden BCD996XT.
Discontinued models, but ones that still can be found through dealers or on the used market include (hh= handheld, b/m= base/mobile): Radio Shack Pro-96 (hh) or Pro-2096 (b/m); Uniden BCD396T (hh) & BCD996T (b/m).
If you're unfamiliar with trunked radio systems, start with this article. There is a wealth of information in the Wiki on this subject.