Needs

• Before purchasing a do-it-yourself alarm system, determine the security needs of your house. Measure the square footage or get a look at the architect's blueprints if you can. Your system must cover the whole property, or least every room you want protected. Count all of the entryways on the ground floor -- doors and windows -- and locate positions for sensors on the jambs. If you want to protect your front and back yards, look for locations for motion-activated floodlights and include them as part of your system. Finally, find a good spot in the house for a control panel. It should be near your primary entryway, close to any required power source (such as an electrical outlet) and out of plain sight if possible.
  
  

Mounting

• One you have purchased a DIY alarm system, pay attention to where you mount each component. Sensors on doors should be placed near the top corner farthest from the hinges; window sensors should be placed in the same manner or on the bottom of the window where it opens. Entry sensors have two components: one on the door or window and one on the jamb. When the entryway is closed, they should be in contact with each other; when it opens, contact is broken and the alarm goes off.
  Motion detectors should be placed in important rooms (i.e., rooms containing valuables) and key points such as stairways. Mount them high up on the wall with a view of the entire area, free of obstructions. If you're setting motion detectors outside, make sure the floodlights illuminate the entire area and that the sensors are sensitive enough not to be triggered by local wildlife or neighborhood cats.
  When mounting your system, pay close attention to the range of each component and its distance from the central control box. If you place it outside that range, it won't be able to activate the alarm. Also, since most DIY alarm systems require batteries, check yours regularly and replace them when necessary.