How does an home security alarm system work?

An Security Alarm System can work with different detectors  or alarm accessories, and it usually has auto-dial or sms features. When a detector (eg. door magnetic contact) or an accessory (emergency button) trigger the alarm, the security alarm system can activate the siren (if installed) to give out loud sound to alert your neighbors and then auto-dial to the pre-set phone numbers / call center monitoring station to notify the alarm event and information. The alarm can also send sms notification to the pre-set phone numbers to report details of the alarm event and information.

A basic security alarm system usually consists of the following devices:

1. Alarm host (control panel): The central unit of the alarm system which is connected to phone line or has GSM connection (now for double protection, many alarm system use GSM plus PSTN). Alarm setups can be customized by user or installation company. User can control arm or disarm status with the alarm host. The alarm host can send out signals to siren, make auto-call, or send sms notifications to alert the user, call center, or neighbour about the alarm event.

2. Motion detector: It can detect human presence within the detectiong range. When motion is detected, the device emits a signal to the alarm main unit to set off the alarm.

3. Door Detector (or door magnetic contact): It can detect opening or closing of any door or window. When door detector is triggered, the device emits a signal to the alarm main unit to set off the alarm.

4. Smoke detector: It is used for fire detection triggered by particles in smoke. When smoke is detected, most smoke detector models can give out loud sound and LED light indication, and send a signal to the alarm unit to set off the alarm.
2. Keypad or remote control: You can arm, disarm, or trigger emergency panic with the use of keypad or remote control. With the use of keypad and remote controls, the user can store the alarm host in a private secure place and operate the alarm host with the keypad and remote controls instead.

5. Siren: During an alarm event, the siren receives signal from alarm host and give out loud sound. Some siren models also provide stobe light feature. This can help warning the intruder to leave the property and also notifying any person in the property (for partial arm use) or your neighbours.
There are many different kinds of detectors that can be added to the security alarm system: pemergency button, glass break shock detector, IR beam detector, gas detector, etc.