Home Control System Alarms

The alarm status has two states and this is used to drive two sounders ('Internal Alarm' and 'External Alarm') based upon the house status:

  • On
  • Off

The alarm sounders are used for both intruders, fires, etc. When the house is occupied the internal alarm is generally used but, this depends upon the cause of the alarm. When the house is unoccupied the external alarm sounder will also go off. The HCS also has the ability to send SMS messages. It will send an SMS alarm when the mains power is interrupted or when a temperature sensor alarms.

The alarm can be switched on and off via a number of interfaces. These all result in a 'Command' events being received by the Home Control System (HCS).



Our alarm system is implemented as a Java class and it has the ability to control the hardware elements described here.

The function to turn the alarm on returns a human readable String, which shows whether the request was successful or why it failed. The turning on of the alarm can fail if sensors show that the house is not secure, e.g. the garage door is already open.


The alarm system uses the following digital outputs and these are all exposed via a distribution board:

Alarm Status

This is a 12V dc signal that provides indication of whether the alarm is on or off. It is used to power a number of LED indicators and as an input into several other home automation components.

Internal Alarm

External Alarm

Alarm Strobe

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