There are two types of Alarm Sirens. These are Inside and outside sirens. Outside Alarm Siren An Outdoor Alarm Siren is one which is placed outside the main living area or house. Many areas have a noise ordinance, In this case you should avoid putting your alarm outside, unless you are on a ranch where you need to know what's going on while your out in the barn. Inside Alarm Siren An inside siren is one that simulates a doorbell and placed high on a hallway wall, or a large siren is often placed in your return air vent. This will let a burglar know that they have violated an alarm so that they will run out of there. It will also let you know that your system has been violated so that you can release the hounds, load your gun or hide under the covers, whatever you select as an appropriate response. Visit our website for more: http://www.elementsecurity.com.au