The purpose of a Door Propped Alarm is to sound an alarm when a door has been left open after a pre-determined period of time – a function that is deceptively complex. The motivation for this function is usually that a door is left unlocked or open when it should be closed and/or locked. Many access control systems include Door Propped Alarm capabilities, but stand-alone Door Propped Alarms are also available.
First, to clear up a common misconception, a Door Propped Alarm is not an exit alarm.
An exit alarm is a relatively simple device that screams when a door is opened. Usually it is equipped with an audible local alarm, a cylinder, keypad or credential reader for reset and authorized bypass, and a door position switch to tell the alarm when to scream. In recent years the exit alarm has grown more sophisticated, incorporating timers for automatic reset, delayed arming and other complex functions.
A Door Propped Alarm must accomplish a more complex set of operations because of the variety of user needs and expectations. A lot of this variety stems from vocabulary issues. For example, many users will refer to a door as being “closed” when they really mean, ‘locked.’ A true Door Propped Alarm will have the flexibility to accommodate these varied expectations.
The condition that creates the need for a Door Propped Alarm is the need to leave the door open for a period of time, but no longer. For our discussion, we’ll call this period of time the Authorized Open Period. This is the most important time segment a Door Propped Alarm needs to track.
The next time segment that a user may want the Door Propped alarm to track might be what could be called the Pre-Alarm state. Typically in this state the Door Propped alarm will change the state of one or more relays. These relays can be used to notify other equipment to create a warning sound, lock other doors, or for many other functions. The warning sound is useful because it allows the user to close to door before the Door Propped Alarm goes into full alarm. In the Pre-Alarm state, the Door Propped Alarm could be set up to automatically reset when the door is closed and/or locked.
The Alarm State may or may not be a timed function, that is, it may have the ability to self-reset after a pre-programmed amount of time that would begin when the door is closed and/or locked, or it may require manual reset at the door by key or other credential. In the Alarm State, the Door Propped Alarm may have an on-board siren or may change the state of a relay to sound an external alarm.
In order to work, a Door Propped Alarm needs a door status switch. Depending on what the user wants the Door Propped Alarm to do, it also may need a lock status switch. If the user wants to sometimes leave the door open or unlocked without the alarm going off, some kind of secure access control, such as a key switch, keypad or credential reader, will be necessary to temporarily bypass the Door Propped Alarm. If the user wants to require that the alarm be silenced and reset at the door for extra security, a key switch or other secure access control will be needed.
To get an even better idea of the functionality of a Door Propped Alarm, go to Securitron’s web site and search out the installation instructions for their DPA-12 or DPA-24 Door Propped Alarm.