Optex used (maybe still do) make an exterior motion with audible announcements...can't remember what it actually "said" or if it was customizable.
Visionics makes (or used to) a SP-3 recordable siren driver (you need a speaker) that you could record whatever you wanted on it...20 seconds(?). You could probably rig something with that on 20P - several ways to do this.
I used to have fun with these things...making stupid announcements to piss off my kids: Mah!! Susie's bothering me. Maaahhhh Jimmy's bothering me! (over and over again @ 15 watts) And I'd bring it with me on road trips..of course it also pissed off the wife.