The alarm panel is the base for all security systems.  Typically the brand name and model number are listed on the front cover; outside or inside depending on the manufacturer.  Inside the panel is a circuit board as well as a battery to provide backup power when an outside power source is not present.

Keypads are the way that a person interacts with a security system, similar to the way a keyboard interacts with a computer. Typically keypads are mounted just inside the main entry doors of the house (ie. the front door and garage door).  Sometimes you will also find one in the master bedroom.  If a house has multiple keypads, any button press on one will correspond to the others in the house as well.

Motion detectors are used as a backup to the sensors on the perimeter doors and windows.  They provide an additional layer of security by triggering the alarm if motion is detected inside the house.  If a window or glass door is broken and used as an entry point without it being opened and setting off the sensor on the frame, the motion sensor will activate the alarm when the intruder enters into the room.  Pet immune versions are available for animals up to 50lbs.

The siren is the voice for the alarm system.  When the alarm is set off, the siren is triggered and will continue to sound for a set amount of time, or until the alarm is disarmed.  There are outdoor versions available also so that neighbors can become aware of an alarms activation if the homeowner is not present.

Keyfobs allow you to arm and disarm the security system from outside the home. They work similar to the keyless entry on most cars.  Depending on the model, some offer other functions as well, like opening an overhead garage door or activating lights.

GSM communicators send alarm signals via cellular instead of traditional analog phone lines.  This way if the phone lines are being serviced by the communications company or are otherwise damaged, the alarm still has a clear path for communicating. Some models allow users to log into their security system to arm, disarm, check sensor status, and many other features.