They are probably like Charlotte, Concord ,Fayetteville and Winston-Salem
There stations are alerted through MOSCAD which means you will not hear any tones across the P-25 system.
Concord has an old VHF frequency of 154.175 Mhz. however it is mainly used for on scene simplex haz-mat operations.
Charlotte used to back in the early 70's, 80's and 90's had a 5 channel UHF fire channel system and Winston-Salem had a two channel UHF system. Both systems have since been depreciated and no long used.
I know that Charlotte Fire doesn't even have a license anymore for their UHF stuff. Winston Salem still holds a license for their UHF stuff.
The only thing Charlotte Fire uses UHF for is on scene Haz-Mat communications and that frequency was one of the old UHF fire ground channels. There isn't even a licensed anymore.
Since these departments do not rely on volunteers there is no need for them to keep and maintain a VHF or UHF paging system.
Guilford uses 453.750 Mhz. for station alerting of Greensboro Fire Stations also for alerting volunteers as well.
I think you will see in the future that all big city paid fire departments will be alerting this way. Now the cities that rely on volunteers will need to keep a frequency available for alerting volunteers.
Maybe if Marshall reads this he can give you better insight as to how the City of Durham Fire Stations are alerted.
Hope this helps
David