There are several types of motion sensors that each detect motion a little differently, with pros and cons for each. By ensuring lights are only on when needed, motion sensors are an easy addition to lower energy costs without needing a complete lighting overhaul. They’re ideal for rooms where lights are accidentally left on, such as offices, or rooms that you often enter with your hands full, like laundry rooms or supply closets. However, not all motion sensors are created equal. There are a couple different types and even more technologies to choose from depending on where and how you need to use them.
Active Sensors
Active sensors use infrared energy, radar waves, or other methods to detect changes in the rooms they cover. The three most common active sensors are microwave, ultrasonic, and tomographic. Ultrasonic sensors are the most used type in lighting and emit sound waves higher than a human can hear although dogs, cats, and the occasional fish can. Microwave sensors emit microwave pulses. This type of sensor is extremely sensitive and is often used in security systems. However, since they can sometimes “see through” non-metallic objects and walls, they are prone to false alarms if not accurately calibrated. Tomographic sensors emit radio waves and are typically used in commercial areas that need a high level of security since they can cover a very large area. Once installed, an active sensor sends out pulses of energy and measures the time it takes for those energy pulses to bounce back when they hit objects in the room. It’s similar to how a bat uses echolocation to see at night. These sensors are not restricted to line of sight and can detect minor movements. However, they are prone to false alarms. Because of this perpetual back and forth, these sensors consume a lot more power than passive sensors.
Passive Infrared Sensors
There is only one kind of passive sensor: passive infrared (PIR). This type of motion sensor detects changes in infrared radiation, also known as heat, emitted by any and all warm-blooded creatures as well as the sun. PIR motion sensors contain a thin layer of pyroelectric material and two slots, which is what reacts to the IR radiation. The sensor remains idle while both slots are detecting the same amount of heat: the calibrated ambient amount of the room. When a person or large enough animal walks through the covered area, it creates a “positive differential” charge between the two slots. This charges are what triggers the sensor. PIR sensors can be calibrated to go off only at certain heat levels, so small fluctuations don’t cause the lights to come on. This prevents the sensor from triggering when small animals enter the room or when the sun rises and warms the room. The coverage for PIR sensors is directional and limited to line-of-sight, so make sure no part of the space you want detected is blocked by partitions or shelves.
Dual Technology Sensors
Dual technology, or dual-tech motion sensors combine ultrasonic and PIR sensing technology. These sensors are less likely to cause false alarms and are typically used in areas where using just one technology isn’t viable, such as offices, classrooms, and rooms with high ceilings or tall furniture. Dual-tech sensors only turn the lights on when both the ultrasonic and PIR sensors detect occupancy, but require just one technology to remain on to help ensure the lights don’t turn off while the room is occupied. This way the small movements like someone typing is picked up by the ultrasonic waves, but the person walking past the door in the hallway is ignored.
Occupancy vs Vacancy
Lighting motion sensors come in two main types: occupancy and vacancy. Occupancy sensors automatically turn on the lights when the sensor is tripped and turn off after a programmed amount of time of no movement. This type of sensor is best used in high-traffic rooms like bathrooms and restaurant pantries. Vacancy sensors, also turn the lights off when a room is vacant and no motion is detected, but you must manually turn the lights on when entering. Conference rooms and rooms with large windows that get plenty of natural daylight most of the day benefit from this type of motion sensor.
Detecting an intrusion is one of the basic principles of a security system, and for this, there must be a device that is capable of detecting a presence to emit the appropriate alarm signal. But to be effective, it must be installed strategically and at significant points so that they can fulfill their function. And the best way to do all this is to know how does a motion sensor work, since the security and reliability of an alarm system depends on it.
What is a motion sensor
A motion sensor is an electronic device made up of several sensors capable of detecting movements that occur within its range. Once this happens, they develop a consistent action that can range from alerting a telephone, a watchman that is connected, or simply activating an alarm by emitting a signal. They can also be used in other areas such as those consisting of putting other types of systems into operation, such as turning lights on or off or in air conditioning, ventilation or home automation installations.
In this article we will focus on those intended for security and to know how does a motion sensor work, the first thing is to know the different types that exist.
How does a motion sensor work depending on the type
Understanding how a motion sensor works can only be done by taking into account the type of design it has and how it receives and emits its energy. These are the ones we can find on the market:
- Infrared sensors: use infrared lights that detect changes in temperature. This occurs when there is something that cuts the beam of the rays that it projects and there is a significant variation in the heat of the environment, such as the one that originates from a person’s body.
- Vibration sensors: they detect the vibrations produced, they are the most used in car alarms, where they transmit an alarm when the vehicle is hit before an intrusion into it.
- Photoelectric sensors: They use photoelectric beams, or lasers, that are transmitted in several directions and that activate the alarm when one of them is interrupted.
- Acoustic sensors: detect the energy that is produced when a sound originates. They are placed in windows that identify when the glass is broken to transmit the alarm signal.
- Ultrasonic sensors: they usually use a frequency of 30 kHz. They emit waves that bounce off walls, windows or furniture and when they are interrupted, they activate the alarm for which they are programmed.
Also, in some circles they are classified as passive or active motion detectors (PIR) according to their type. The former are activated when they detect a sudden change in heat or temperature, while the latter emit energy in the form of waves, light or sound and are activated when they detect a variation in them.
How to regulate a motion sensor
These devices have very good versatility thanks to the regulation possibilities they present. Thus:
- They can be regulated according to their scope: In this way, their scope of action is delimited with great accuracy and allows very exact areas to be controlled.
- They can be regulated based on time: These models are activated only when they detect a presence and then stop working, obtaining great savings in energy consumption. The equipment that have this type of regulation are those that present great efficiency and optimization of use.
- Depending on their luminosity: They are known as the crepuscular ones, and they have the option of being able to work at night or during the day, as appropriate.
Where are the motion sensors placed?
If you have understood how a motion sensor works, its placement can be extremely logical: they should be placed in those places where it is likely to identify any type of movement or alteration, as is the example of PIRs, which are usually focused on passageways , corridors and doors and windows.
But you also have to take into account that it must be connected to the alarm, so it is necessary to make its connection. In another article on our blog called how to connect a motion sensor to an alarm we explain in detail how to do it.
Motion sensors can be extremely reliable indoors, but they can also be installed outdoors, although in these cases, they have less performance than those indoors. The most suitable for this are:
- Dual technology passive motion detectors.
- Infrared barriers for perimeter protection.
- Microwave barriers to protect perimeters. Better than the previous ones, since they are made up of two components: one that emits the waves and another that interprets the possible interruptions that may arise.
Other uses
Although our article is focused on security, motion sensors can have different applications, such as lighting an area when it detects the presence of a person.
Another very common one is in ventilation, and as a most characteristic example is its installation in a bathroom where, upon detecting a presence, it starts the extraction to ventilate properly and eliminate bad odors and humidity. It is also not uncommon to find this type of detector that, at the same time, turns on the lighting in these rooms.
Presence sensors are also widely used to activate two-flow inlets or dampers in multizone demand-controlled ventilation, or DCV, systems. In this way, MIN/MAX or ON/OFF ventilation systems are available in a very simple way.
In short, understanding how a motion sensor works is knowing that they have the ability to measure the stimuli they receive to determine if they are likely to be a danger or not. For more information, contact MICROSEGUR and our technicians will evaluate which is the most suitable for your home or business alarm.