I'm gonna get robbed...

Simon III. Source it from a Dealer local to you or purchase it from an online store that actually provides the support you might need to set it up.

Yep. But the OP wants to use a fob remote, which means he can mount the panel in a fairly secure location and not worry about someone smashing it to stop the signal. Besides, I believe Simon comes with an optional remote keypad so you don't have to use the main unit to arm and disarm the system.

Looks like the Alegro can use a FOB as well - yes?

oops - but it appears that it can simply dial a central station and not call with a special message. With the Simon can you disable the horn at the panel? And instead use the plug in X-10 horns to sound alarm?

Simon has remote dialer also and can call you with message about what is going on.

Yep.

And instead use the plug in X-10 horns to sound alarm?

I wouldn't use *any* X-10 component as the only means of alerting you to a problem with your security system. X-10 is unsupervised and isn't considered reliable. Simon will output to a remote siren AFAIK.

Simon's internal system can simply be unplugged. However, this is the same siren used for entry/exit delay beeps and whatever else, so you won't be reminded to turn off the system when you come home.

Either way, the OP mentioned extremely loud sirens. Neither the Simon series or the Allegro has anything close to loud, especially when you can just hold your hand, a pillow, etc. over it. I've never installed external sirens to either system, so I can't speak on those though.

For such a cheap place, maybe neatly surface-run white wire would be OK? In that case, you wouldn't be limited to wireless.