You are currently browsing the Door Hardware Genius blog archives for July, 2011

Understanding Door Security Monitor Switches

A number of different kinds of switches are available to help you keep track of whether or not your door is shut and / or locked.  Here are some of them:

Door Status Monitor Switch

A door status monitor switch changes states when the door is opened or closed.  Typically this is accomplished by using a magnetic reed switch, either surface mounted or concealed in the edge of the door and door frame like the one shown at right.

How a Magnetic Reed Switch Works

The magnetic reed switch is typically installed on the door frame and the magnet that activates the switch is typically installed on the door.   Inside the magnetic reed switch, a thin piece of steel – a steel ‘reed’, if you will – is held in position by the attraction of the magnet when the door is closed.  When the door is opened, the magnet is taken away from the switch and the spring tension of the “reed” causes it to spring back against the other contact, changing the state of the switch.

Most magnetic reed switches are normally closed – “closed loop” – but are also available normally open (“open loop”) SPDT (single pole double throw, or “form C”) or DPDT (double pole double throw).

The Purpose of the Door Status Monitor Switch

The door status monitor switch is used to notify remote devices that a door is open or closed.  Typically these remote devices are burglar alarm panels or access control system controllers.   It does not tell you if the door is locked, just if it is closed.

Request to Exit Switch

The request to exit switch, also known as a REX switch, is so named because it is usually connected to the request to exit contacts on an alarm panel or access control board.  It is used to notify an external device that someone is exiting through, or wants to exit through, a door.  REX switches come in a wide variety of configurations, from push button palm switches engraved “push to exit” to switches concealed inside exit devices.  A motion exit sensor is also a form of request to exit switch.

Request to exit switches are available with a wide variety of contact configurations and with or without electronic or pneumatic time delay.   If the switch is being used as a means of egress for pedestrian traffic, it will need to comply with life safety code.  Life safety code varies from locality to locality as governed by your local AHJ – Authority Having Jurisdiction – that is, your local building inspector or fire marshal.

Latch Bolt Monitor Switch / Strike Monitor Switch

I write about Latch Bolt Monitor (LBM) switches and Strike Monitor Switches because they somewhat overlap.  Both are designed to monitor the position of the latch bolt.

Some LBM switches are inside locks and others are in electric strikes.  From inside the lock, they monitor whether the latch is extended or depressed.  When located in an electric strike, they monitor whether or not there is a latch bolt present in the keeper.

Pictured at right is Securitron’s line of inexpensive strike monitor switches as examples of strike monitor switches.  Several companies offer like products.  Strike monitor switches are an easy way to monitor if there is a latchbolt (or some other object) present in the keeper.   Several companies, such as Von Duprin, offer heavier duty monitor strikes.  Monitor strikes are sold as a finished unit that includes as strike and a switch whereas strike monitor switches are aftermarket add-on units.

Magnetic Bond Sensor / Bond Sensor

Magnetic bond sensor and bond sensor options refer to electromagnetic lock applications.  Many manufacturers offer Bond Sensor or Magnetic Bond Sensor as an option.  What this does is allow an electromagnetic lock to notify some external device that its holding force is below spec.  Authorities are alerted and the situation is addressed.

Maximizing Effectiveness

To maximize effectiveness of door monitor switches, it is best to use both a door status monitor and some kind of lock status monitor as well, and this is why:  because monitor switches can be fooled.  A door status switch will tell you if the door is open or closed – unless it has been altered to tell you the door is closed when it is not.  Also, a door may be closed, but not locked.  If you have a latch bolt monitor or magnetic bond sensor in place as well as a door status switch, you will know if the door is closed but not locked.

This is the center of this knowledge:  to know that the door is shut AND locked.




How to Choose a Door Closer

To intelligently choose a door closer for your application you have to know certain facts:

  • Does the closer need to comply with ADA opening force guidelines?
  • Is the door an interior or exterior door?
  • What is the door width?
  • Will the closer be mounted on the push or pull side of the door?
  • Where on the door will the door closer be installed?  How much room is there?
  • Are there any special circumstances like wind, positive or negative pressure, etc.?
  • You may also need to know the door handing.

ADA Reduced Opening Force Guidelines

American Disabilities Act (ADA) reduced opening force restrictions are enforced by the Authority Having Jurisdiction in your locality.  In some localities or applications ADA requires a maximum opening force of 5 lbs. and in others a maximum opening force of 8.5 lbs.  Most closers on the market today can be field adjusted to comply with these restrictions, but to do so you need to have a door pressure gauge.

I am mildly acquainted with two door pressure gauges.  One is the model DPG by HMC and the other is the ADA/FG by LCN.  Apparently there are a lot of initials involved in door pressure.

Door closers are also available with reduced opening force meant specifically to comply to ADA standards.

Manufacturers usually print a disclaimer that says that a door closer adjusted to ADA maximum opening force may not have enough power to shut the door.  This is often true because perhaps recommended spring strengths for different applications are the result of perhaps a century of innovation.  Manufacturers know that a force greater than 8.5 pounds may be necessary to close a door.

Interior versus Exterior

When speaking about door closer closing force, we say that a door closer is of a certain size.  Door closer size does not refer to actual dimensions, but to spring strength.  Historically, door closers are available in sizes 1 through 6 – 1 being the wimpiest and 6 capable of exerting the strongest closing force.

A size 4 closer is usually recommended for an exterior, 3-foot wide door, whereas a size 3 closer is deemed appropriate for an interior door of the same dimensions.  The assumption here is that the exterior door is more likely to be expected to close a door against a wind or negative or positive air pressure.

Door Width

If you look at a door hung on butt hinges and equipped with a door closer from above, it looks something like this:

View from the Ceiling


You see from the illustration that the door closer closes the door by exerting force on a point about eight or ten inches from the hinge side of the door.  To see what this means, go to a door with no door closer.  Open it.  Now put your hand a foot from the hinge side of the door and push it closed.  Pretty difficult, isn’t it?   If your door was wider, it would be even harder to close from that point.  This is why door closer size – that is, spring strength – is determined by the width of the door rather than the height.

For a three foot wide exterior door, you would normally adjust your door closer to be a size four.  For a four foot wide exterior door you would adjust your door closer to be a size five.  Therefore, if you have a four foot wide exterior door, you had better buy a closer that can be adjusted to a size five.

Push or Pull?

Different arms are required for different applications.  On doors that swing out, where the closer is mounted on the push side, the closer is mounted in a top jamb or parallel arm configuration.  If it is mounted on the pull side it is mounted in what is called a ‘standard’ installation.  (There are other ways to mount a closer on the push side, but parallel arm and top jamb are the most common.)

See manufacturer’s literature for more information, or check out my article on Door Closer Basics.


If you have a glass and aluminum storefront kind of door, you may have a space issue as regards your choice of door closer.  If you have a hollow metal door with no window hung in a steel frame, chances are you will have no space issue.

You need to figure out what door closer will fit.  To do that, measure the space where you would like to install it and download installation templates or instructions from manufacturer’s web sites.  Check the dimensions to see if the closer you have selected will work or not.

Or you can measure your door and frame and consult a door hardware professional.

Special Circumstances

I have installed door closers in some fairly challenging environments.  One, for example, was on a four foot wide, eight foot high, two and a quarter inch thick mahogany and glass door.  In addition to the size of the door, the location was also challenging – right across Beacon Street from the Boston Common where the wind could race across the open ground and dash itself against the door to its heart’s content.  Also, the front of the building had settled over the century or so of its existence, and leaned decidedly inward.  The door opened inward, and, left on its own, would swing sedately inward to 90 degrees if not latched.

In other words I had to install a door closer that would close an extra heavy door, uphill, in a wind.  I actually got one that would do it about 95% of the time.  For this application I chose the most durable, powerful, adjustable door closer I knew at the time:  the LCN 4041.  If I did the same job today I would probably choose an LCN 4011 or a Norton 7500.

A big, beefy, versatile door closer is not a cure-all.  For example, sometimes the 4041 is just too big, or templated too close to the hinge.  The point is that you must look at all the details of your door before you buy a door closer – not only how it is made and its size, but its environment as well.