We have 4. A few years ago, someone cut a piece of glass out of our back door, so my eldest son bought and installed 2, one to cover the back yard and the other over the front door, focused on the ground right outside the front door and window, where the car was when my husband was alive. A year or 2 later, he talked us into another 2, one covering the passage at the side of our end terraced, the other over the front door again, but focused on the road upwards from the house. They do give you that extra secure feeling, knowing that if anything occurs you can rewind them and hopefully see the culprit. I`m afraid that I`m no help regarding makers names or the technical side of things, that bit goes right over my head!