The best design is one that blends the layout of the house, the way you will use the system, and also the actual threat (i.e. points of access). Start with the doors, then go to first floor windows. Don't forget the door from the garage into the house, of the basement, if there is one. Motion sensors are not generally active in the "stay" mode, so you don't set off you own alarm. You can avoid putting a sensor on every window by using glassbreak sensors, as they can cover a large area (assuming windows are closed and locked). In other words, there is some real thought that goes into this - and the good DIY alarm companies are very skilled at talking you through it, so you get what you need, and install it all correctly. You can find them on-line - but check all the reviews you can find.