The main purpose of a home security system is to keep your property and the people inside it safer. Harm may come in the form of a burglary, home invasion, fire, flood, or other environmental disaster. Most home security systems can monitor for all of these. These systems use a combination of sensors that communicate over radio frequencies or wires to a central hub, which then communicates with the outside world using a cellular connection or occasionally a landline. The hub is generally a touch screen mounted to your wall or a small box placed on a counter or in a cupboard.
The sensors are installed strategically around your home at entry points such as doors and first-floor windows, as well as in hallways and high-traffic areas. They detect when a door or window is opened or closed, when someone is moving around in your home, or both. When the system is armed, it sends an alert to the hub after a sensor is triggered. The hub then sounds an audible alarm, sends you a notification (a phone call, text, or a notification on a mobile app), and can alert a monitoring center if you have professional monitoring.