It took a couple tries to get one that worked properly, but eventually I did. It worked great for about 8 months, but eventually began to lose it's ability to sense movement. It is now literally on just the opposite side of the door and turned to maximum sensitivity and it only works once in a while. When it worked, it was great, many people thought I had gotten a dog. The repetitive barking wouldn't be noticed unless someone stood listening for a while. Most people would move on once they heard the first few barks thinking there was a dog. Considering we're in the tech generation I can't believe another company has not developed one, it's an awesome idea and when it works, it's perfect. This unit is just not built to work longer than a few months. Very unfortunate.

I am very happy with this product. I have been using it for about two months now. I set it up so that it covers my home front door and patio door (you will likely need to make minor directional adjustments to determine the best location for the device). It senses through my front and patio door. It also seems to pick up 360 degree movement. The dog bark is realistic and sounds like a pretty big, angry dog. Perfect.

This product surprised me as being better than I thought. It has some flaws but overall for what looks to be a 20 year old dated product does deliver.
It does have a sensitivity feature as you approach REX, he barks, and as you get closer he barks more violently, however, there are not enough barking variations, and if you listen long enough you can easily tell it is a loop sounding exactly the same.
The feature that I really do like it is the duel mode, where you first hear the dog barking and then it sounds like the house alarm has gone off.
Warning, it's 300ft range is questionable. I have a steel door, and you definitely do not get the full 300ft range.

I have two of these. They are the best on the market, but there is a flaw, in that the speakers seem to bottom out. My friend and I thought it was the audio recording that was clipped but it turned out to be the speaker or electronics bottoming out (the volume level is too high so you hear a weird vibration noise). As a result, you hear the dog barking once, you get closer, it barks a few times, you get closer still, and it goes crazy barking, but that crazy barking is a bit louder and you hear buzzing due to this engineering failure, and it lets you know the dog is fake. That is the details explanation of all this "It sounds fake ... NO it sounds REAL" argument you keep seeing in these reviews. If you lay this thing on its side (try both sides, it varies) and put the speaker against something to restrict it (one thing I tried was putting tape around the speaker) the buzz gets less. If you turn it way down, the lower volume also gets rid of the buzz, but then it's too low to really work well as a dog, so you would have to plug it into an amplifier or mic it, but it doesn't have output holes to plug into anything, so that's my next idea. When I get a chance, I'm going to make an "Output" jack on it, by soldering wires from the speaker to a headphone jack from Radioshack. The dog sound TERRIFIES my pet dog, and he's big, and through a thick wall it sounds 90% real, even with the buzz, but if I can get rid of the buzz this product will be idea.

Positioning this thing is also a pain in the backside, since my doors have steel in them and it blocks the sensor. I have to put it a few feet back and to the side of the door, and then turn the sensitivity way up, so that it does such a wide area that it reaches around the door. If I put it right next to the door, on the floor, against the wall, it won't see people at the door and will only see people to the side of the door. Get creative with range settings and location and play with it for a half hour, trying it at different ranges and locations until you find what works for your door. And it is annoying that you can't avoid it going off as you move around the house, but I don't care because my use is for vacation when nobody is in the house.

We have 3 of these and was planning on 1 more for all 4 corners of our garage but then we installed a wi fi camera with intercom system on our front porch and we lost our most important perimeter alarm access point. The ED-50 Rex Plus now barks constantly so we had to move it. So hopefully our porch camera system will warn us as good as Rex did because it does a really great job! Doesn't work thru metal but thru brick and mortar just fine. TC Life Safety.com has a good video to watch explaining no wifi or microwaves or it will false bark. Great service thru Amazon and will be keeping all 3 purchased here, just wanted to share this is not a wifi friendly product. If we resolve the issue I will update. If anyone else has overcome this , please share :) Thanks!