How Do Automatic Doors Work?

Most automatic doors use motion detection sensors or optical sensors, which are installed on the sides of the door, to trigger the opening/closing of doors.

Many people tend to believe that automatic doors are an invention of the modern world, but it may surprise you to know that automatic doors have been around for almost half a century. Over time, these doors have become more technologically sophisticated, but the idea has been around for quite a while!

All automatic doors, irrespective of their type or design, consist of sensors that help trigger the opening/closing of doors when the need arises. Let’s look at the various kinds of sensors used in automatic doors:

Pressure sensors

In the 1960s, ‘control mats’ were used as sensors to detect the approach of pedestrians. These mats detected changes in the weight/pressure on a specific area of the ground in front and back of the gates. If the weight that a particular area experienced was more than the set limit (the ‘trigger limit’ was set lower than the average human weight), then the doors would open.

automatic doors

A person would have to stand or walk over the pressure-sensitive area due to its strategic placement (Image Source: Wikipedia)

The advantage of using this kind of system was, and still is, that the doors remain open as long as there is pressure on the mat, or in other words, if there is a person standing/walking near the doors. This not only makes it easy for swift entry/exit, but also prevents the doors from ‘closing in’ on an individual.

Motion detectors or optical sensors

These days, however, most automatic doors use motion detection sensors or optical sensors, which are installed on the sides of the door, to trigger the opening/closing of doors. These sensors, as their names imply, detect or ‘look for’ motion in front of the gate. In these sensors, motion is detected by a microwave beam (10.5 GHz) produced by an antenna that is installed on the door header and generally points in the downward and outward direction.

motion detector

A typical motion detector (Image Source: Wikipedia)

These sensors are quite effective, but have one major shortcoming: they can only detect motion. Therefore, a person standing still or walking very slowly (like senior citizens) might not be detected, which can lead to accidents.

Infrared sensors

These specialized sensors use infrared technology to trigger the opening/closing of doors. These sensors detect changes in temperature in the area surrounding the doors, so when an individual approaches the doors, their heat signature is detected by the sensors, which cause the doors to fly open!

infrared sensors on Automatic doors

How Infrared sensors on automatic doors work

Note that these sensors work efficiently by themselves, but different sensors are often used in various combinations in a single system to prevent hiccups or oversight. For example, motion sensors do their job of triggering the opening mechanism as soon as they sense or ‘see’ motion in front of the doors. However, if the individual is moving too slowly or standing still near the doors, the pressure sensors detect the weight of the individual and prevent the doors from closing until the weight is relieved, i.e., the person moves away from it or pass through the doorway.

How do the doors actually open?

After the sensors detect the presence of an individual, the job of actually opening/closing the doors must be completed. Sensors are connected to an electronic drive train, which is attached to the panels of the door through an auxiliary drive or a cog wheel. The auxiliary drive is connected by rubber belts that regulate the opening and closing motions of the doors. At the bottom of these doors are rollers that allow the doors to slide so smoothly.

Automatic doors are incredibly convenient and quite safe these days, yet work is always being done to discover better and smarter designs. I don’t know about you, but personally, I would love a door that opens with a snap of my fingers or a simple spoken command… that’s the kind of future I’m looking forward to!


  1. Wikipedia
  2. Reference
  3. Sensors journal
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About the Author:

Ashish is a Science graduate (Bachelor of Science) from Punjabi University (India). He spends a lot of time watching movies, and an awful lot more time discussing them. He likes Harry Potter and the Avengers, and obsesses over how thoroughly Science dictates every aspect of life… in this universe, at least.

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