Also, the pager will lock onto the first site it finds. Since it won't be scanning multiple sites, you'll only hear the traffic on that site. For example, if you are somewhat near the St Clair County simulcast system, and the pager locks onto that site, you'll hear the St Clair County traffic, but may not hear traffic occurring only on the Madison County site or the other area sites.
Same in reverse, if you say, cross over into Collinsville, it may lock onto Madison County Simulcast and you'll no longer hear most traffic from St Clair County, since most of those talkgroups only stay on that site (usually).
The only way to get around this, is to create another "Knob" with each site, so you can pick the site that you want to be on specifically.