Ok, there's tons of different setups, and even dozens of types of gear from this one manufacturer. But I bought a simple receiver with one transmitter kit, and added 3 more motion detectors. Skylink motion detector basic kit HA-318: http://www.amazon.com/Skylink-HA-318-Household-Alert-Motion/dp/B000EN69DU/ref=pd_sxp_grid_pt_1_1 Extra motion detectors HA-434A: http://www.amazon.com/Skylink-PS-434A-Motion-Sensor/dp/B000KL0MZC/ref=pd_cp_hi_2 All the gear at the website: http://www.skylinkhomesecurity.com/ They don't work well with animals, which set them off. But I did try one inside the car, and it seemed to work ok for the distance between the car and the receiver inside the house. I think they say these are not for outdoor use, but I'm using mine outdoors, mounted up high under the gutter and overhang, pointed at the driveway, cars, bikes, etc. And that's why the cats, dogs, raccoons, and coyotes set them off at night. Sometimes insects will manage to set one off, if it's up close in front of the sensor. edit: I take it back, they are meant to be used indoor or outdoor. I just checked. Lots more geeky stuff indoors, but let's just say "Open my door and they are screwed". They would just run away. I never have trouble around my place anyway, for some reason bad kids tend to stay away...