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