The primary function of a door stop is to prop open a door or to protect the wall when a door is opened all the way. A security door stop, however, is a mechanism which either prevents a door from opening or sounds an alarm when a door is opened. Some versions do both. Security door stops can be large units to be installed in a residence or small, portable units made for apartments or hotel rooms. A security door stop can withstand more force than a dead bolt in some cases.
Even the best security alarm systems can fail or a perpetrator can disarm the electronic unit. A security door stop, while not a replacement for monitored alarm systems, provides a near fail-safe backup. Most home intruders are not equipped to apply the amount of force necessary to break or disable a security door stop.
One type of security door stop is a large steel pole which is placed under the door handle at a 45-degree angle from the floor. The pole serves as a wedge between the door handle and the floor and prevents the door from opening. Some models can withstand up to 3,000 lbs (1,360 Kg) of force.
Another type of handheld security door stop is much smaller. It is shaped similar to a regular wedge door stop one can place at any door, but on top of it is a spring-loaded plate which slides under the door. When pressure is applied to the plate, the alarm sounds until the pressure is released or the battery dies. The smaller wedge type of security door stop can sometimes be placed a few inches inside of the door instead of underneath. In this capacity, the door stop can function much the same way as an old-fashioned chain lock. A door can then be opened only to a certain point, allowing the home resident to see who is outside.
When purchasing a security door stop, one must take into consideration several factors. Some models are adaptable to different flooring surfaces, from hardwood to carpet, while some are not. In addition, some units may not work with sliding glass doors or French doors. Most units that are equipped with an alarm will run on batteries which will need to be replaced, but some stronger models do not have an alarm built into it. Some models are adaptable as window alarms as well.