I use a Nexus 7 tablet android device running LANnouncer and for most sounds (I just live in a single story 1500 sq ft house), the tablet itself is loud enough but you could plug in an external speaker or connect via bluetooth. I have connected it to my Amazon Echo for example and it can get quite loud.
LANnouncer can play MP3 files which I haven't tried yet but using Big Talker, I can use a chime sound, siren sound, doorbell sound, or just voice via TTS. Using Rule Machine, I can use the TTS function for additional voice with its rules that I create.
All this can happen with a simple Open/Close contact switch on the door which I currently use. I also have a motion detector aimed at just the front door area so people don't even have to ring the door bell and I know that someone is at the door. I have to admit though that using a motion detector outside is usually not recommended due to lots of false alarms. I've tried to narrow my motion sensing area but I still do get the occasional false alarm.
For the door bell part, I haven't utilized it but you would have to either replace the existing doorbell with a Z-wave or Zigbee button but I hear there are some inherent problems that due to battery saving measures, they often require two presses, one to wake them up and another press to actually do something. I think the same goes for the Aeon Labs Doorbell switch. If you could somehow figure out a way to tap into your existing doorbell to a contact switch would probably work best. Here's an old thread that touches briefly on that topic:
Finally, another option is to go with a pressure sensitive mat under your Welcome mat: