Last Updated on March 4, 2022 by Alarm New England

When installing your security system, should you invest in a motion sensor or a window sensor? In many situations you should consider both, but that doesn’t mean you might not have specific areas that have a unique requirement.

Most security systems include two pieces of equipment designed for intrusion detection: motion sensors and window sensors.

It’s not immediately clear what the difference is between these two devices, so here’s a quick guide to explain:

  • How motion detectors and window contacts work
  • The advantages and disadvantages of both

Motion Sensors

Motion sensors are built to detect when someone is moving around in your residence. Primarily, a motion sensor works by sensing movement and body heat when a person passes near it or walks through the range of its radar.

motion sensors as part of your home security system

These days, most motion sensors are small in size and wireless. That means that you can easily install them anywhere in your home without distracting from your decor or having contractors drill holes in your walls to run wire everywhere.

Motion sensors use a number of technologies to determine whether someone is currently in motion inside of your home. At its most basic, a motion detector is simply going to compare the previous status of a room to its current status. So when developing your home security plan it is critical to understand the strengths and weaknesses of motion sensors and how that factors into your home security.

Below are some of the pros and cons of motion detectors:


  • A single motion sensor can cover a wide radius (typically an entire room), so it doesn’t matter how the intruder enters the house. Once he passes within the range of the sensor’s infra-red beam, he’s immediately detected.
  • Motion sensors are proven to be effective at leading to apprehensions. With the aid of motion sensors, police are much better able to capture burglars red-handed inside residences.
  • Most motion sensors come wireless and can be installed in a variety of locations with relative ease.
  • Motion sensors can be more cost-effective for rooms with many windows that would require several sensors to protect.
  • A motion detector can alert you immediately if there is movement is detected.


  • Motion sensors are only triggered when an intruder crosses their sensor range. If not set up correctly, the motion sensor may have blind spots.
  • When a motion sensor is set up incorrectly or uses low-quality parts, there’s a higher risk of false alarms. So they often have the highest number of false positives, which can be frustrating and lead to reduced sensitivity to potential threats.
  • Some motion sensors only detect motion at certain intervals. So because it does this at intervals, it can sometimes miss things.
  • Pets in general make motion sensors a liability. Even pet-immune motion sensors aren’t totally pet immune. Cats are especially known to climb onto raised furniture, appearing to the sensor to be much larger than they really are.

What are window sensors?

Window sensors are for protecting windows from unauthorized entry. With the aid of a circuit between a magnet and a sensor, they detect when windows are opened (but not broken, as that is best handled by a glassbreak detector).

window sensors to secure your perimeter against intruders

Windows can be an area of your home that presents the greatest risk. Often locking doors is top of mind but securing windows can be tedious and be forgotten and a necessary precaution.

Protecting your windows is essential because intruders tend to try windows next after testing the strength of your doors.


  • Window sensors function with high levels of accuracy, provided they are correctly installed, meaning fewer cases of false alarms.
  • Window sensors are cheaper on a per-part basis.
  • When used with other types of home security, window alarm sensors provide an essential piece of securing your homes perimeter.


  • A secured window has to be opened before the alarm can be activated. It will not activate if a burglar smashes through the window or gains entry through another means.
  • Securing each and every window with a window sensor can be costly for larger houses.
  • Loud sounds or someone slamming a door can set off a window alarm with a false alarm.

When should I use motion detectors?

Motion sensors are excellent at detecting when an intruder is already inside the house. They should be placed in parts of the house that an intruder would have to pass through to get to other parts of your house, especially in areas where there are no movements such as a whirring fan or rustling curtains. Due to their sensitivity, they need to be placed in carefully designated locations to prevent false alarms.

If there are pets in the house, it is better to get motion sensors that are adequately calibrated for pets, so their movements won’t set it off. Bedrooms, living rooms, lobbies, and hallways are apt locations to install motion sensors.

In home motion detectors

When is it more appropriate to use window sensors?

Window sensors discourage opportunistic burglars from gaining entry without resorting to smashing your windows, which can alert people in the vicinity to their presence. They are more fitting for houses where there is motion in the house when you’re not in it (e.g. pets or children).

Large dogs or cats of any size are a good enough reason to opt for window sensors, but they’re also ideal if you arm your system at night before going to bed. Family members will want to have the freedom to walk around the house at night without the risk of tripping any alarms.

Window sensors should be installed at every ground-floor window and any upper-floor windows in the house if there are adjacent trees or buildings that would grant them easy access.

If you’re only using window sensors, you should also add glassbreak detectors as well for added protection, as window sensors don’t go off when someone hurls a brick through the windowpane. For large windows or sliding glass doors, glassbreak sensors are a must-have.

Carefully consider the type of window you’re trying to protect so that your sensors that will best fit what you’re looking for.


As property crime rates continue to go up year-to-year, so will demand for new and improved ways to protect our homes. Home security devices are one of many things homeowners can do to improve their peace of mind.

As you build a comprehensive security system that is integrated into your home automation, you should use different types of sensors and detectors in different areas. Your hallways, bedrooms, and living rooms might have motion detectors installed, while your outer windows may have both contact sensors and glass breaking sensors installed.

To learn more about what you can do, check out the Ultimate Guide to Home Security.