A motion sensor is a device that detects moving objects or people. It’s usually a vital component of a system that either alerts the user of movement or performs a specific task. They play a big part in security systems, automated lighting control, home control, energy efficiency, and other such practical systems.
These electronic motion detectors have an optical, microwave, or acoustic sensor in addition to a transmission for illumination (most of the time). There are other kinds of sensors too. For example, a passive sensor detects an object that’s moving by an emission or reflection. This means that it can either be emitted by the object or by other factors, such as the sun or a radio station that’s strong enough. The changes in the device’s proximity in the optical, microwave, or acoustic fields are interpreted by electronics that have features of the technologies listed below. A lot of the low-cost ones can only detect movement up to 15 feet. There are specialized systems that have longer ranges, but they do cost more. Tomographic motion detection systems use radio waves that have high enough frequencies to penetrate through walls and other things (including objects in a different location than the actual transmitter), giving them a larger range.
These devices are used both residentially and commercially. Businesses use them to activate automatic doors when customers get close enough to the entrance or exit of the building. They can also be used to turn on streetlights or lights inside a building for a certain amount of time (for the length one would be expected to be in the area). Only having the lights on for a set amount of time when someone walks by helps save a lot of energy. Another way these are used is to detect the presence of someone that could be an intruder. When that happens, an alarm may be triggered to alert you and/or a security camera may start recording to catch the possible intrusion.
Sensor Technology
Here are some types of motion detection that are used frequently:
Passive infrared (PIR) – These are sensitive to people’s skin temperature. This is done by reading the black body radiation at mid-infrared wavelengths emitted from a human body in contrast to background objects that are at room temperature. It doesn’t emit anything, which is why it’s called a passive infrared. This differs from an electric eye in the sense that an electric eye will detect emotion when a person or car interrupts a visible or infrared beam.
Microwave – The principle is that of Doppler radar, similar to a speed gun. A stream of microwave radiation comes out of it and phase shifts in the reflected microwaves (caused by the motion of an object toward or away from the receiver) result in a heterodyne signal at a low audio frequency.
Ultrasonic – These waves are at a frequency humans can’t hear. They’re sent out and by doing that, reflections of objects close by are gathered. Heterodyne detection of the received field shows motion in this method too. This doppler shift that was obtained is at low audio frequencies (for walking speeds) too because the ultrasonic wavelength of a centimeter is basically the same as those used in microwave motion detectors. There is a drawback to this type of sensor and that is the fact that they can pick up motion that you don’t want coverage of by using reflections of sound waves around corners. This can be great if you’re using the sensor to turn lights on and off when people come into the area, but in other cases, such and an automatic door, you’d want one that would only sense movement directly in front of or behind the door.
Tomographic motion detector – These pass radio waves from node to node of a mesh network and sense the disturbances to said waves. They have a big range because they are able to sense through walls and other objects.
Video camera software – Because there are so many inexpensive digital cameras that can shoot good video footage, it’s now possible to use one to detect motion using a software. This works especially well for filming during times that someone is moving in the area since there’s no need for hardware other than the camera and computer. This can be used in an area that is lit or be used in conjunction with near-infrared illumination (at wavelengths undetectable by the human eye) to detect motion in the dark.
Gesture detector – With the aid of machine learning algorithms, infrared lighting elements as well as photodetectors can support digital screens that detect hand motions and gestures.
Area reflective – Uses infrared rays created by an LED to detect if an object is in the designated area and to measure the distance it is away using the rays’ reflection.
Vibration – These obviously detect vibration. You can either buy or make one, though the homemade ones may be unreliable. The ones created at home would consist of a small mass on a lever. When it vibrates, it would be activated by a switch to sound an alarm.
Dual-Technology Motion Detectors – A lot of motion detectors now use several different technologies to sense movement. These do have their pros and cons. While they can reduce false triggering, the chances of any movement being detected are less, increasing vulnerability. To explain this, you should keep in mind that many of these dual-tech sensors use both a PIR sensor and a microwave sensor and that both sensors have to trip at the same time. This works pretty well considering that lighting changes will only trip the PIR and something such as moving branches will only affect the microwave. The downside of this comes when an intruder is able to find a way to trip only one of the sensors. Often PIR technology is combined with a different model for increased accuracy and less energy usage. PIRs don’t use as much energy as microwave detectors do. Therefore, a lot of sensors are calibrated so that when the PIR is tripped, a microwave sensor is also activated. If the microwave sensor detects an intruder, it also sounds an alarm.
Kinds of Motion Sensors
Driveway Motion Detectors – If you have a lot of visitors, you may want to purchase one of these. They’ll alert you when someone rides a bike, walks, or drives up to your house. They can also be good for detecting movement in shed, patio, or pool areas. There are a couple things to consider before purchasing one though. For one, the range is important. This is because the sensor can’t be too far away from the receiver. Most of the standard ones will work for a normal driveway (about 400 feet), but if your house is farther away from the street, you’ll want a special long-range one that will work for up to half a mile. The second thing to consider is the response type. Some will just alert you with a doorbell like sound when motion is detected (to just let you know someone is there and you should be ready for company). Others are better for security as they will let you networks several sensors into a walkie-talkie to tell you where your property has been invaded. If you really want to scare intruders off, you can have it trigger something that’ll drop something scary (like a clown or something) in front of them.
Motion Flood Light – These are a really great option for both scaring off potential intruders as well as providing a safe and visible pathway to your home for its residents. Some models allow you to choose the kind of light you’d like. It could be a harsher floodlight or a more welcoming lighting situation. You’ll want to find one with either a timer or a photoelectric cell so that it’ll shut off during the daytime when you really don’t need it.
Motion Detector Guard Dog – These are really cool because they create the barking sound of a dog without you actually needing to have one. Some are fancy enough that they’ll even change the bark depending on how close (or far) it senses that the person is. In addition, you can change the sound to more pleasant ones (such as a rainforest) when you’re expecting guests.
Security Alarm Systems – Purchasing indoor motion sensors helps complete your home security. They are an important part as well because as soon as the intruder gets in your house, every movement will be caught as he/she begins to go to and steal stuff. There are a couple things you should consider before you pick whether you want black and white/color or how big of a range you want it to cover. First off, you’ll want to choose whether you’d like wired or wireless. Wireless are very nice because you can find that perfect spot on the wall that’ll catch the burglar for sure and not your pet. However, if your house is big, you’ll want to go with a wired system because wireless systems have a maximum range of 400 feet. Another option is a pet-safe detector. These have been designed to ignore pets up to a certain weight. Otherwise, you can mess around with the placement, testing, and masking on other types to make them pet immune.
(You can also place contact motion sensors on your windows or doors that will sound an alarm if they’re opened.)
Best Ways to Mount Sensors
Some systems require a professional to install, while others are DIY home security systems. Various packages will give you prompts though or will provide a representative you can call who will help you set it up.
It’s important to remember that these systems won’t be perfect. False alarms do happen and are typically caused by electrical failures, poor application engineering, user error, lightning, faulty equipment, and power surges. Insects, plants, and animals can also trigger them.
To avoid this, follow the instructions that come with the sensor and keep the following tips in mind.
- Keep PIR sensors 10-15 feet away from sunlight, heating vents, and radiators. If there’s a sudden surge of heat or a cloud passing by, it could trip the sensor.
- Put sensors in areas of higher foot traffic such as stairwells or hallways (also known as “choke-points”). This way, the sensor will be tripped no matter where the intruder is going. Usually, burglars go for the master bedroom so you’ll want to put a sensor near there or in any other rooms that have valuable items (like a study, for example).
- You should walk through your house and find the route you think someone would take if they broke into your house and place cameras in that path. It is important to remember that motion sensors can detect between 50 and 80 feet. Most intruders come in the patio, garage, front, or back door so you’ll also want to put cameras there too.
- Movement is best caught when the intruder goes by parallel to the sensor. Therefore, you don’t want to point the camera directly at where someone would be walking, but rather parallel to it.
Other Uses for Motion Sensors
Motion sensors are used for more than just home security. Industrial fields use them to shut down dangerous equipment if someone gets too close to it as well as to keep track of the number of products made on an assembly line.
They’re also used in the following ways:
- Opening and closing automatic doors
- Turning on and off automatic faucets and toilets
- Turning on lights when someone enters a room
- Controlling ATM displays
- Opening automatic ticket gates
- Running parking meters
In terms of a security system, motion sensors aren’t just a plus, but rather are vital. If they didn’t exist, there wouldn’t be a way to detect an intruder.
Some More Tips
- Don’t face an indoor motion sensor at a window. This is like setting up for failure. It won’t detect humans but may be tripped by car headlight or movement of sunshine.
- Once again, don’t put your motion sensor in a place that’s drafty or one that has a vent. The warm or cold air blown could trigger it and cause a false alarm.
- Motion sensors have their own blind spots. PIR ones may not detect something moving straight toward them. You may want to do some testing and install a couple sensors perpendicular to each other in order to catch everything.
- Clean off your outdoor sensors. If dirt or grime gets built up on them, they may not function properly anymore.