I'm not a security expert (just DIYer) so do plenty of research... but I set up a basic system with MiCasaVerde.
Any of the z-wave networks might do what you want, but MCV sounded the most customizable, and I was willing to do some of the programming. If you want it to be easy and simple, you can say: if it's night, and the motion detectors sense motion, make the alarm go off (maybe only sound the alarm for a few minutes unless you really want to get the neighbors' attention).
It's not 100% reliable. In my mind it's 95% good and that's good enough given all the tradeoffs. I just want something that (almost always - and hopefully that'll be never...) will make the standard intruder decide that he's made a mistake and head elsewhere. If an FBI agent wants to rob us, I figure we've got bigger problems. We're not interesting targets - I mostly did it for when I'm away and my wife is home alone.
I can tell you that whenever I forget to disarm the system and I go wandering into areas that are monitored, the alarm always goes off. But it's a computer, and glitches are possible.
Equipment you'd need:
- A "brain" or z-wave hub (MCV or Smarthings or whatever brand you choose). Maybe $100 or so
- Motion detectors (and/or window/door sensors). About $40 each
- A siren. Maybe $50
I've also set up light switches and do the porchlights on timers (and have a few motion detectors set outside, even though they're not built for that - they're under the eaves). All that is controlled by the z-wave hub.
Edited to add: you can have it send you text messages if you're a halfway decent programmer. There's a really good user group to help figure it out. So you could notify a neighbor or other "helper" if you have an alert, or just find out which motion detector went off.