What Is a Motion Sensor Alarm?

A motion sensor alarm is a device that uses optical, microwave, or acoustic sensor technologies to detect motion around your home or workspace; and to let you know that there is a physical security event that shouldn’t be happening. Motion sensors are also sometimes known as motion detectors.

A complete motion sensor alarm system has a few main components. The first is a motion detector, which is the most outwardly evident part of it (that’s why the whole motion sensor alarm system is sometimes only known as motion detector). This motion detector is generally a passive infrared sensor, and is just a generally white block with a semi-translucent panel that receives IR radiation, and detects changes over time.

Image result for motion sensor

The second component of a motion sensor alarm is the electronic control panel. This is usually an integrated panel that control multiple sensors, and interprets the signals from the motion sensors and translates them into usable signals.

Finally, this is all managed from a mobile or a desktop app. The best modern systems are cloud-based, or at the very least integrated with some sort of online platform, which is the layer that you will interact with when looking at the data from your motion sensor alarm.

A complete motion alarm system can also be connected to a motion sensor camera. The camera sets off when the alarm is activated to send a visual message to the responder. The responder can consequently take the most appropriate action for each specific intrusion. Although motion sensors’ main purpose is to warn the homeowner of unwelcome “visitors”, such as burglars or thieves, they are also used for other situations where motion is the kickoff event, such as the automatic opening of doors, or the automatic turning on of lights.

Motion detectors either provide safety or create an easier lifestyle. Typical alternative applications of motion sensors are smart lightning, detection of poaching animals, and activation of door locks and automatic gates in residential and commercial premises. You can use your smartphone to implement affordable motion detectors that cover up to 15 feet of distance. Advanced and more expensive motion sensor models extend to larger surfaces and can keep you feel safe on large-scale properties and spacious business buildings.

Why Is It Important to Have a Motion Sensor Alarm?

Assuming the primary use of motion sensor alarms is not too complicated - whenever there is a movement in the vicinity of where you live or work, you can use the motion detector to stay alert of what is going on when you are, and when you are not there. Motion sensor alarms are the principal guards of perimeter security, forming the outer layer of protection.

A motion sensors can warn you to act before things get out of hand. For example, you’ll be able to call the police before there is greater property damage or, even worse, a bigger risk to yours, or to the lives of your loved ones.

Motion sensors are resourceful and easily installed. They can be placed at vulnerable points of your house or apartment and help you sleep safe and sound. Since they are small and not as detectable as video surveillance systems, intruders are less capable of locating and disabling them.

When a motion sensor is programmed to activate a motion sensor camera, the camera keeps a video record of the event. Activating lights to scare off intruders is the least a motion sensor alarm can do. While you are waiting for the police, the combination of a light, a siren and an irretrievable door lock can disempower impostors keeping them under lockdown.

Small children and pets are not to remain at home unsupervised, even when there is someone to look after them, such as a babysitter. A motion sensor alarm can ward off a “no access” area; for example, prevent your kids to get into the garage or the basement.

‍You can supervise the handymen without sacrificing a day off from work

Installing motion detectors is not only about having a modern high-response physical security system, but also about energy efficiency. There are electronic access control systems that combine physical security and home automation. You can manage how safe your home is remotely, from a smartphone. Functions of integrated motion sensor enable setting personalized smart light schemes and room temperatures. In this way, you can prepare a pleasant and safe environment from your car on your way home.

What Are the Various Types of Motion Sensors?

A conventional way to categorize motion sensors is by using the receiving and emission detection mechanisms as criteria.

Passive motion sensor alarms are based on infrared technology and only observe movements by passive heat detection.

Active motion sensors are based on radar technology. They work by transmitting, as well as by receiving radio waves that boomerang when hitting a moving object.

Combined motion sensor alarms use several technologies, but are not applicable to all areas. Some work better outside than the others, and vice versa. Many access control systems use a couple of them to provide better protection.


‍Radar technology is used in active motion sensor alarms

Here is how are motion sensors commonly categorized:

  • Passive infrared sensors (PIR). These motion sensor alarms sit with a bird’s eye view of the room, and detect changes in the IR signature of a room over time
  • Active infrared sensors. Also known as tripwires, these emit an IR beam from one side of the room to the other, that detects an intruder when it gets interrupted
  • Ultrasonic detectors. A different paradigm, these work by emitting ultrasonic sound waves to detect motion
  • Tomographic motion detectors. One of the coolest innovations in motion sensor technology, these are comprised of a mesh of radio detectors around a room that detect changes in the ‘fabric’ of the mesh caused by people moving through them
  • Gesture detectors. These are a subcategory of IR or camera motion sensor alarms that detect specific motions

Hybrid motion sensors apply several technologies. Case in point, a motion sensor camera can be integrated into inside and outside access control systems, and the technology in use will depend on whether it is dark or light.

Tell us about your project

Which type of security system do you need?

Calculate price
Tell us about your project

How does each of these motion sensors work?

Common motion sensor alarm systems work by using the following technologies:

1. Passive infrared motion alarm sensors detect the body temperature of the moving objects. When the access control system is in the armed mode, it can sense skin temperature and body radiation that differs from the inanimate objects in the background. The passive technology in infrared sensors works like a protective mesh around the premises that is activated once a set temperature threshold is surpassed. They are great indoor solutions.

2. Active infrared motion sensors emit electrical signals that connect to a light detector. When the electric beam gets cut off by motion, it triggers the motion sensor alarm sound. They work better outside.

3. Microwave alarm sensors cast out microwave pulses that can cover larger areas than infrared technology, assessing the pulse reflected off objects in motion.

4. Ultrasonic motion detectors use both modes: active and passive. They use high-frequency sound waves that go back to the transmitter and remain uninterrupted unless there is an intrusion. This is when the alarm gets activated by buzzing a sound.

5. Tomographic motion detectors are used in multiple nodes form a mesh network, thus being adequate for larger surfaces. Tomographic motion detectors can pass through walls and other physical impediments.

6. Gesture detectors use elements from infrared light technology and photodetectors to enable a digital screen to observe hand gestures by applying machine learning technology. They work with smartphones.

Getting to know infrared sensors

Simpler versions include activation by vibration. Although these are easy to install, they might be unreliable. Many advanced motion detectors use wireless technology as it is no trouble setting it up. Combined technologies trigger fewer false alarms, but they can also pose a risk because of the additional elements necessary to alert the responder.

Infrared radiation works on the lower end of the electromagnetic spectrum and is therefore invisible to the human eye. The infrared section of the electromagnetic spectrum is found between the visible waves and the microwaves. The infrared wavelength is between 0.75 and 1000µm and is separated into three regions:

  • Near-infrared - from 0.75 to 3 3µm
  • Mid-infrared - from 3 to 6µm
  • Far-infrared - higher than 6µm

Astronomer Herschel discovered the infrared section of the electromagnetic spectrum with the famous prism refraction experiment.

Infrared radiation is a characteristic of all objects that have a temperature higher than the absolute zero (0 Kelvin or -273 Celsius). Such objects have thermal energy and can emit infrared waves. IR sensors usually use infrared lasers and LEDs with infrared wavelengths.

In order for the thermal energy to reach the IR sensor, it must use a transmission medium. Compatible mediums are the atmosphere, vacuum, or optical fibers. Optical lenses made from combinations of metals and minerals, such as quartz, calcium fluoride, polyethylene, germanium, aluminum, and silicon are used as radiation convergents. The converged or focused radiation is afterward detected by infrared detectors. Infrared detectors must additionally use pre-amplifiers to strengthen the signal.

Infrared technology is widely used for commercial purposes for:

  • Night vision devices.
  • In astronomy, to detect objects in the universe by telescopes and solid-state detectors.
  • In military activities for missile tracking.
  • In art restoration to analyze paintings and discover hidden painting layers.
  • For tracking nanoparticles in living organisms.

IR sensors also find use in studying the weather, gas detection, petroleum examination, and water analysis, as well as in medicine for anesthesiological purposes. IR sensors are used for security as part of access control systems.

PIR motion sensors

PIR motion sensors are specific IR sensors, also called passive infrared sensors or pyroelectric sensors. The acronym PIR stands for “passive infrared”. PIR motion detectors are intended for a specific use of infrared radiation - the part which detects the infrared wavelength coming from the environment. They are inexpensive but very sensitive to detect and indicate whether a person is in or has left a detection field.

The PIR motion sensor is made from a pyroelectric component (a combination of metal and crystal) and additional electrical elements, such as circuitry, resistors, and capacitors. The passive IR sensor is typically protected by a metal shell and has a silicone window to let the radiation pass through it. Most PIR sensors are rectangular in shape, have a sensitivity range of up to 20 feet. In terms of power supply, they belong in the range of 3.3V - 5V input voltage.

The sensor in the PIR motion detector consists of two halves because its purpose is not only to detect infrared waves but also to indicate a change as a signal for motion. The sensor is idle when there is no motion in the detection field. However, when a person or another living thing that radiates heat, such as an animal passes in the field range, it produces a positive differential change in the first half on its way in and a negative differential change in the second half of the sensor on its way out. To be able to detect and pass subtle signals, the PIR motion sensor includes a lens or concretely, more lenses integrated as smaller sections in a larger component called fresnel lenses.

PIR sensors can be used to detect the movement of people, animals, and objects.

When mounted on the wall or on the ceiling, PIR sensors can be used in an access control system to communicate to the central board that a movement in the area has been noticed. Infrared sensors then trigger alarms and report the event to the owner, the law enforcement, or the security contractor, depending on who is in charge of taking the action. The sensors can also instigate video recording or activate physical barriers to prevent the intruder from escaping.

PIR motion detectors can also be placed in thermometers to measure the temperature of a distant moving object. Emergency teams use PIR sensors for rescue purposes, for example, if a person has been lost on a mountain or for medicinal purposes to detect the skin temperature. They are placed in TV remotes and computer mouses to manage specific functions, such as on and off or scrolling.

Which type of security system do you need?

How many doors or entry points do you want to secure?

Do you need to install an access control system?

kisi logo

Starting a new project?

Learn everything you need in this downloadable guide.

Starting a new project?