I also have the outside areas of my property alarmed so the alarm gets activated as soon as someone starts snooping around the outside. This is a great idea, as it is more likely to scare off intruders if they haven't even broken in yet. Plus saves the repair costs of busted window/door frames.
When the alarm calls you up, there is very sensitive microphone that you can use to listen in to help determine if someone is inside or whether the cat has someone set it off. I had to upgrade the PIR in my lounge to a dual technology sensor that adds microwave detection as my cat would manage to set of even the pet safe PIR when jumping down of the top of the couch.
You can also add several numbers for the alarm to call just in case you have your cell phone off and don't respond.
Th only little annoyance with the system I got is the audio chrip used to indicate that you've armed or disarmed the system (using the keycahain remote) goes through the external siren which is quite loud and unpleasant, so is a little embarassing. There is a mute button you can press first which I use a night. You can tell by a flashing LED in the siren whether you've sucessfully armed/disarmed the unit. This LED is hard to see in daylight so you need the audio to acknowlege that you've push arm (and not disarm by mistake) and that the button had transmitted properly. Alternatively you can use RFID or keypad, though I use the remote so I can arm/disarm without getting of my car.