My son gave me Guardline's for my birthday last year. Two remote sensors and two monitors for the house. One upstairs, one downstairs. They're Ok so far. I need to adjust the sensitivity on the outside sensors because they've been really good at notifying me of birds, the cats coming and going, leaves blowing, dust from a car/truck going by, anything that doesn't matter at 3am! Because of that, I've gotten pretty indifferent to the alarm going off. That defeats their purpose.
The Guardline has somewhere around 30 different alarm tones so you can program that many remote (outside) sensors to one inside monitor. They have two different outside sensors with different coverage specs. One covers 50 feet, the better one covers something like a 1/4 mile. It takes some time to get them positioned correctly. They have a small red light that lights up when they're triggered. That's probably not so good if someone is really paying attention. The alarm would be activated but I read where some had their sensors stolen because of the red light. The outside sensor looks like a little brown bird house on mine.