When it comes to automatic door sensors, there are two primary options that you can choose from: microwave sensors and infrared sensors.   But what exactly is the difference between these two sensors? And which would make a better door sensor?

These two types of motion sensors are the most common ones you’ll find in commercial buildings, and it’s not hard to figure out why– both work efficiently at detecting moving people and objects, and immediately opening automatic doors.

To answer these questions, let us first break down how each one works.

The Infrared Sensor

The infrared sensor works by measuring the infrared light radiating from the objects in its field of view.

 All objects with a temperature above absolute zero emit heat energy in the form of radiation. This radiation cannot be seen by the human eye, but can be detected by electronic devices like the infrared sensor.

The infrared sensor conducts an analysis of a room or surrounding areas, and looks for a change in infrared energy. Should it detect a change, such as the presence of a moving person in the proximity, it will emit a pulse activating the automatic door sensors, which in turn prompts the doors to open.

Infrared sensors are also known as Passive Infrared Sensors. ‘Passive’ here refers to the fact that these sensors do not emit or generate energy for detection purposes; they work simply by detecting infrared radiation emitted or reflected from objects.

The Microwave Sensor

The microwave movement sensor works quite differently to the infrared sensor. It applies the Doppler effect in that it sends out microwave signals and measures the length of time it takes for these signals to bounce off of surrounding objects and return to it. This echo time is what it uses to calculate the distance of stationary objects around it. It first establishes a baseline room or area analysis to detect the current distance of all surrounding objects. When something comes into the detection area thereby interrupting the microwave signals and altering the echo time, it perceives this as a change in distance from the object and this sets off its trigger.

The microwave sensor works much like a RADAR or SONAR system, sending out signals to measure its distance from objects. But the microwave sensor can also detect motion through wood, plastic, glass and most other construction materials except metal. Metal acts as a shield, creating dead zones behind them. This can be both an advantage and disadvantage to the microwave sensor.

Now that we know what the difference is between the two, it’s time to answer the question: which is better? The answer however isn’t clear cut:

Comparison

Microwave sensors are highly sensitive and are able to detect motion even through thin walls. In this sense, they are more powerful than infrared sensors. 

But because of their sensitivity, they can easily get triggered erroneously or trigger false alarms. They sense movement in terms of speed and size, and so they can be triggered by things that normally shouldn’t trigger a sensor like trees blowing in the wind, moving drapery or movement beyond walls. Even fluorescent lighting, which emits detectable light particles, can activate the sensor and trigger it.

Infrared sensors on the other hand, are less prone to such false alarms.

 But since they detect movement through heat and light, their performance can be affected by the ambient temperature. Often their sensitivity is compromised when the ambient temperature reaches beyond 35℃. The opposite happens in very cold temperatures wherein they become extremely sensitive. Microwave sensors are more stable in this sense, operating properly even at temperatures as low as -20℃ and as high as 45℃.

Since infrared sensors detect movement through body heat – they are ideal for situations that require defined detection, such as in front of a doorway or down a walkway. But they must be installed in just the right position to provide effective coverage.

Microwave sensors are great for just about any environment. They can provide fine motion-sensing whether in high heat, a large indoor commercial area, or large outdoor area that may be awkwardly shaped. This makes them one of the most versatile of sensors.

Microwave sensors often have a longer lifespan than infrared sensors. They’re also one of the oldest and most relied on sensor technologies, but can be more expensive to run since they require more power.

Since microwave sensors work at intervals – meaning they first emit signals and then receive them- it’s possible that someone or something moving fast enough may not be detected.

So which sensor would be better for your automatic door? Generally, infrared sensors are more suitable for smaller, more compact entryways and well-controlled, indoor spaces, whereas microwave ones are good for large areas. But who says you need to choose anyway?

The passive infrared (PIR) motion detector is one of the most common sensors found in household and small business environments. It offers affordable and reliable functionality. The term passive refers to the fact that the detector does not generate or radiate its own energy; it works entirely by detecting the heat energy given off by other objects.

Strictly speaking, PIR sensors do not detect motion; rather, they detect abrupt changes in temperature at a given point. As an intruder walks in front of the sensor, the temperature at that point will rise from room temperature to body temperature, and then back again. This quick change triggers the detection.

PIR sensors may be designed to be wall- or ceiling-mounted, and come in various fields of view, from narrow-point detectors to 360-degree fields. PIRs require a power supply in addition to the detection signalling circuit.

Motion sensors can:

For some parking meters

Passive Infrared (PIR)

Detects body heat (infrared energy). Passive infrared sensors are the most widely used motion in home security systems. When your system is armed, your motion sensors are activated. Once the sensor warms up, it can detect heat and movement in the surrounding areas, creating a protective “grid.” If a moving object blocks too many grid zones and the infrared energy levels change rapidly, the sensors are tripped.

Microwave (MW)

Sends out microwave pulses and measures the reflection off a moving object. They cover a larger area than infrared sensors, but they are vulnerable to electrical interference and are more expensive.

Dual Technology Motion Sensors

Motion sensors can have combined features in an attempt to reduce false alarms. For example, a passive infrared (PIR) sensor could be combined with a microwave sensor. Since each operates in different areas of the spectrum, and one is passive and one is active, Dual Technology motion sensors are not as likely as other types to cause false alarms, because in order for the alarm to be triggered, both sensors have to be tripped. However, this does not mean that they never cause false alarms.

Area Reflective Type

Emits infrared rays from an LED. Using the reflection of those rays, the sensor measures the distance to the person or object and detects if the object is within the designated area.

Ultrasonic

Measures the reflection off a moving object and sends out pulses of ultrasonic waves.

Vibration

These can be purchased or easily made at home. Detects vibration. A homemade vibration sensor uses a small mass on a lever, which is activated by a switch to an alarm when it vibrates. Homemade motion sensors can work, but they can also be unreliable

Wireless Motion Sensors

Today, most motion sensors are wireless. Wireless sensors are very easy to set up. They do not require drilling, and they communicate with the other security system components wirelessly.

Pet Immune Motion Sensors

A passive infrared sensor can be set up to ignore animals up to a certain weight. A dual technology motion sensor is more resistant to false alarms caused by animals because it requires two sensors to be triggered in a manner determined by the manufacturer. They can be set up to ignore a large animal or multiple small animals without setting off a false alarm. Some pet immune motion sensors have a sensitivity level that can be adjusted for families with very active animals.

Video Motion Sensors

Combines video cameras with advanced signal processing. Some recordable motion sensors start recording when they sense motion. Cameras controlled by motion sensors can save you memory storage by not recording hundreds of hours of useless footage—they only capture the important stuff. circuit

Best Practices for Mounting Sensors

Keep in mind that motion sensors aren’t error-proof, and there are instances in which there could be false alarms. False alarms are usually caused by electrical failures, user error, poor application engineering, power surges, lightning, and faulty equipment. They can also be triggered by animals, insects, and foliage.

The best thing you can do to increase the effectiveness of your sensors and prevent false alarms is to read the instructions that come with your sensors. Also, consider the following motion sensor placement tips:

Keep PIR sensors 2-4mtrs away from heating vents, where the sunlight shines in, and radiators. If a motion sensor detects a swift change in heat, even that of a cloud passing quickly over direct sunlight shining into your living room, it could be tripped.

Place motion sensors at “choke-points”—areas where people have to walk through, like the stairwell or main hallway. That way, an intruder will trip the sensor regardless of where they are headed. Intruders usually go right for the master bedroom, so put a sensor near that room or other rooms where you have valuables, like the study.

Best Practices for Mounting Sensors

Assess where intruders are most likely to enter, and what path they would take. Keep in mind that most motion sensors can detect between 15 and 25 meters. Most burglars enter the home through a front or back door, patio door, or garage door, so it’s advisable to place the sensors near those areas.

Find walls that an intruder would walk alongside, like a hallway or narrow pathway that leads to a room.Motion sensors work best when the intruder walks parallel to the sensor, not toward it. For example, in a hallway you tend to walk parallel to the walls, not directly toward them.

Consider the Size of Your Pets

Pet immune motion sensors are only immune to pets when used correctly, and even then they can create false alarms under certain conditions. Many pet immune sensors are rated by an animal’s weight, but in reality, they’re based on height. If your pet likes to practice their high jump, it can set off false alarms.

Best Practices for Mounting Sensors

Don’t Block the Infrared

Motion sensors are like flashlights sending out a beam of light, but with motion-detecting infrared energy waves instead of light waves. Just like a light is brighter closer to the bulb, the infrared radiation is denser nearer to the device and it spreads out the farther away you get.

A motion detector’s waves can’t penetrate through walls or other hard objects like furniture. When you’re setting up your motion sensor, imagine it like a light on the wall. Anything that creates a shadow from light in that position can also block the motion sensor’s ability to cover the shadowed area.

Reed Switches

The hermetically sealed reed switch is a very common type of two piece sensor that operates with an electrically conductive reed switch that is either normally open or normally closed when under the influence of a magnetic field as in the case of proximity to the second piece which contains a magnet.

When the magnet is moved away from the reed switch, the reed switch either closes or opens, again based on whether or not the design is normally open or normally closed.

This action coupled with an electric current (typically at 12V DC) allows an alarm control panel to detect a fault on that zone or circuit.

These type of sensors are very common and are found either wired directly to an alarm control panel, or they can typically be found in wireless door or window contacts as sub-components.

Photoelectric beams

Photoelectric beam system detect the presence of an intruder by transmitting visible or infrared light beams across an area, where these beams may be obstructed.

To improve the detection surface area, the beams are often employed in stacks of two or more.

However, if an intruder is aware of the technology's presence, it can be avoided. The technology can be an effective long-range detection system, if installed in stacks of three or more where the transmitters and receivers are staggered to create a fence-like barrier.

Systems are available for both internal and external applications.

To prevent a clandestine attack using a secondary light source being used to hold the detector in a sealed condition whilst an intruder passes through, most systems use and detect a modulated light source.

Glass-break detection

The glass-break detector may be used for internal perimeter building protection. Glass-break acoustic detectors are mounted in close proximity to the glass panes and listen for sound frequencies associated with glass breaking.

Seismic glass-break detectors, generally referred to as shock sensors, are different in that they are installed on the glass pane. When glass breaks it produces specific shock frequencies which travel through the glass and often through the window frame and the surrounding walls and ceiling. Typically, the most intense frequencies generated are between 3 and 5 kHz, depending on the type of glass and the presence of a plastic interlayer. Seismic glass-break detectors feel these shock frequencies and in turn generate an alarm condition.

Window foil is a less sophisticated, mostly outdated detection method that involves gluing a thin strip of conducting foil on the inside of the glass and putting low-power electric current through it. Breaking the glass is practically guaranteed to tear the foil and break the circuit.

Smoke, heat, and carbon monoxide detectors

Most systems may also be equipped with smoke, heat, and/or carbon monoxide detectors. These are also known as 24-hour zones (which are on at all times). Smoke and heat detectors protect from the risk of fire using different detection methods. Carbon monoxide detectors help protect from the risk of carbon monoxide poisoning. Although an intruder alarm panel may also have these detectors connected, it may not meet all the local fire code requirements of a fire alarm system.

Traditional smoke detectors are technically ionisation smoke detectors which create an electric current between two metal plates, which sound an alarm when disrupted by smoke entering the chamber. Ionisation smoke alarms can quickly detect the small amounts of smoke produced by fast-flaming fires, such as cooking fires or those fueled by paper or flammable liquids. A newer, and perhaps safer, type is a photoelectric smoke detector. It contains a light source in a light-sensitive electric sensor, which is positioned at a 90-degree angles to the sensor. Normally, light from the light source shoots straight across and misses the sensor. When smoke enters the chamber, it scatters the light, which then hits the sensor and triggers the alarm. Photoelectric smoke detectors typically respond faster to a fire in its early, smoldering stage – before the source of the fire bursts into flames.

Driveway Sensors

Driveway alarm systems can be tied into most security and automation systems.

Passive magnetic field detection

Microwave barriers

Microphonic systems

Security electric fence

A security alarm is a system designed to detect intrusion – unauthorized entry – into a building or other area such as a home or school. Security alarms are used in residential, commercial, industrial, and military properties for protection against burglary (theft) or property damage, as well as personal protection against intruders. 

Some alarm systems serve a single purpose of burglary protection; combination systems provide both fire and intrusion protection. Intrusion alarm systems may also be combined with closed-circuit television surveillance (CCTV) systems to automatically record the activities of intruders and may interface to access control systems for electrically locked doors.

Systems range from small, self-contained noisemakers, to complicated, commercial systems with computer monitoring and control. It may even include two-way voice which allows communication between the panel and Monitoring station.

Elements of alarm systems?

Alarm control unit/panel The "brain" of the system, it reads sensor inputs, tracks arm/disarm status, and signals intrusions. In modern system, this is typically one or more computer circuit boards inside a metal enclosure, along with a power supply.

The control panel typically feature a touchpad for easy programming and interaction, is where pass codes are entered to arm and disarm the system, can work on voice commands, and can be programmed to work with wireless remote controls called key fobs.

How does a security system work?

Home security systems work on the simple concept of securing entry points into a home with sensors that communicate with a control panel or command center installed in a convenient location somewhere in the home.

The sensors are typically placed in doors that lead to and from a house as well as easily accessible windows, particularly any that open, especially those at ground level. Open spaces inside of homes can be secured with motion sensors.

Panel Components