Most cameras have sound built into them, with either the camera receiving sound via a microphone, emitting sound via a speaker, or both. Cameras that both receive and emit sound effectively double as intercoms.
While many vendors claim that their cameras have an alarm, these may not emit sound at a volume that would deter intruders. Deep Sentinel’s system has a siren in its base station as well as an alarm feature that will broadcast from a two-way audio system. We have a 46mm speaker for our camera alarm, which makes it as loud as our siren hub.