Home Security 101: Window and Door Sensors

Between different wireless technologies and smart home integration capabilities, home security has gotten pretty complicated in recent years. That’s okay as long as everything works. But when you strip away all the fancy stuff and get down to the most fundamental components of a home security system, you are left looking at window and door sensors. They are the starting point.

Fifty years ago, there was no such thing as wireless home security. Security systems were wired packages that consisted of three primary components:

  • Window and door sensors
  • Motion detectors
  • CCTV cameras.

For the record, CCTV cameras were limited to high-end systems only the wealthy could afford. The average homeowner interested in a security system would have to settle for the motion detectors and window and door sensors. And even at that, motion detectors were optional.

A Simple Principle

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Window and door sensor design is based on a simple principle: maintaining and disrupting contact between two surfaces. The typical window or door sensor is a two-piece unit. One piece is mounted on the window or door, the other piece is mounted on the adjacent jam. Both pieces have magnetic contact points.

When the window or door is closed, contact is maintained between the two pieces. When opened, contact is broken. Now all you need to do is connect an electrical source and you are good to go. Breaking contact sends a signal to the central security hub and an alarm is sounded. It is pretty simple.

Other Types of Sensors

The magnetic contact sensor has worked so well that it is still the primary technology for monitoring windows and doors in a home security scenario. But there are other types of sensors, too. For example, a recent guide to window and door sensors published by Vivint mentions both motion-activated sensors and broken glass sensors.

1. Motion Sensors

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Window and door sensors that detect motion work on the same principle as the previously mentioned motion detectors. They utilize infrared light to detect movement within a general area. Deploying them for windows and doors can detect even slight window or door movement that might not otherwise be triggered by a magnetic sensor.

Motion sensors are considered a step above because they can detect a potential forced entry faster than a magnetic contact sensor. But they are also more prone to false alarms if they aren’t installed and calibrated correctly.

2. Broken Glass Sensors

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Magnetic contact sensors work well enough when an intruder forces a window open. But what if that intruder figures out a home is protected by a security system and chooses to break the glass instead? He can still get in through the window without activating the magnetic contact sensor. The solution is a broken glass sensor.

Vivint explains that broken glass sensors monitor for sound. They can detect the sound of breaking glass, thereby triggering an alarm. It is not clear how breaking glass is distinguished from other loud and sudden noises. Nonetheless, the technology seems to work.

Protecting a Home with Sensors Alone

In theory, it’s possible to protect a home with window and door sensors alone. You could install a DIY home security system with nothing but sensors, being sure to equip all first-floor windows and doors. Given that it is rare for burglars to attempt second-floor entry, you would be fairly well protected. But here’s the problem: window and door sensors only alert you to an intrusion in progress. They don’t do much in terms of prevention.

Window and door sensors also cannot be monitored in the same sense that video cameras can. The end result is that your response time could be slower. That’s okay with burglars who prefer to get in and out quickly as possible. If your response is delayed by even a minute, an enterprising burglar already has a good head start.

Because window and door sensors are limited in their preventative capabilities, a typical out-of-the-box system also includes two additional components: motion detectors and video cameras. Motion detectors have already been discussed. So let’s move on to video cameras.

Video Cameras Enhance Security

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There is little doubt that video cameras enhance home security. That’s why wealthier homeowners wanted CCTV cameras in their systems 50 years ago. They understood that cameras act as a deterrent by letting criminals know they are being watched. In addition, video cameras provide evidence that can be used to track down and prosecute criminals.

Take a house with window and door sensors alone. A burglar who knows the home is equipped with a security system may think twice about trying to break in. But if he sees no video cameras, he may suspect the only impediment to his success are window and door sensors. He now has at least some motivation to take his chances.

On the other hand, seeing video cameras on the home’s exterior changes things. The burglar sees those cameras and knows his chances of getting away with the crime are lower. He can take a shot anyway or move on to another house that is not equipped with video surveillance.

More than Just Property Crimes

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Everything this post has discussed thus far has been related to property crimes. But home security provides protection against other threats as well. Take smoke and carbon monoxide. Both are considered silent killers because they can overwhelm the occupants of a home without them knowing anything. Window and door sensors do no good in this regard.

On the other hand, a home security system equipped with monitored smoke and CO detectors is a safer home by far. An alarm triggered by either device immediately alerts monitoring personnel who can both contact local authorities and alert any occupants inside the home.

The point of all this is to say that window and door sensors are the starting point for home security. They are the foundation on which systems are built. But alone, they only offer minimum protection. Adding other devices makes a home security system more effective.