My gut feel would be to connect the speakers to the camera and let the camera play back the recording. I recall Mobotix supporting this. Anyone?
Sony 6th Gen cameras let you upload three voice alerts and trigger them via events on camera. I think the 5th gen allowed for one voice clip. It can be triggered by any input, motion detection, analytics, or a combination of the above. I don't recall seeing this in a lot of other cameras.
You can use any powered speaker with a line level input. Sony has one. You could probably find cheaper, as well, depending on what kind of output power you're looking for.
I also don't recall VMSs triggering this, but it's not a widely sought after feature so I may be missing it.
That is a different approach then how I had pictured it... I was thinking more of having the VMS or camera triggering an output to some type of music on hold device that had the recording and was connected to the speakers. I like the idea of doing it through the speakers but the cameras are going in right now (Arecont MP dome/bullet cameras). If I had known they would have wanted this feature I would have gone the on camera route initially. I have a call into Exacqvision to see what they say, hopefully its possible. I will let you know what happens but if anyone else has any ideas please let me know and thank you all for the feedback!!!
Inaxsys Security Systems
This is quite easy using Exacq. Their Professional version of software supports Event Linking. You can trigger a relay on any camera to follow a motion detection event on any other camera.You can even require that the event (motion detection) happen from multiple sources to play the audio:
If the camera you are using does not have an output relay then you can use one of Exacq's new USB input/output modules to trigger the output relay to the audio device.
For the audio device, you can use something like this device ( Note: I have never tried this device, I simply found it from a web search. There are some good quality sound devices that exist on the market . You just have to be sure you can trigger the pre-recorded message from a dry contact coming from your camera or the USB input/output module).