There are two main types of security systems that protect your home: monitored alarm systems (video surveillance), and local area systems (so-called "bells only"). The latter are the more basic ones. These traditional unmonitored systems have various types of sensors placed in and around the house: for example, they can be hooked up to doors and windows. Some devices of this type will also include motion detectors. "Bells only" typically include the use of sound alarm that goes off when the device detects a perceived threat.