Wireless motion detectors
Belong to the top draw of choices of home security system products. Being one of the most economical options as well, if installed correctly, they can provide effective security for you home and valuables. Also if you can spend some time in deciding the strategic positions where the detectors are to be placed, such as the living rooms, staircase and entry ways, you can ensure that every inch of your house come under the watchful eyes of the motion detectors and thus can be at peace of mind about your home security.
Types of wireless motion detectors:
There are basically two types of motion detectors, namely, active and passive. Active motion detectors are generally used in shops, grocery stores etc, where they are also used for the automatic opening and closing of the doors for the customers and also for security purposes such as ringing an alarm during an unwanted intrusion. The active motion detectors generally work with radar, ultrasonic sound waves or photo sensors that sense and measure the changes caused to an otherwise continuous beam of light. They are called active detectors or sensors because they emit energy into the environment in the form of light, sound or microwave in order to detect a change in the surroundings when it occurs.
Passive motion detectors are used for most of the home security solutions. They use passive infrared technology to detect the intruders and dont emit energy to the surroundings. They detect any new presence in their range by sensing the temperature. That is, any intrusion coming in will have a different temperature as compared to the current temperature where the detector is situated. For example, human beings generally have a skin temperature of about 93 deg F and radiate infrared energy of a different wavelength than what is being radiated inside the room, which will be at a different temperature, however slightly. So, when they move through a room where the motion detector is installed, the detector senses the change and the alarm are sounded.
Ultrasonic or acoustical type of motion detectors, which were widely used in the 80s, is not preferred anymore. They transmit an ultra-sonic frequency signal which when collided with fixed objects, bounce back in a certain pattern. Therefore a moving object disrupts this pattern, thereby setting off the alarm. A problem with this type of detectors is that when used for a long time, they would burn-in a frequency and if the objects were moved around the room where the motion was located, the detector will not clear due to the mis-match in the frequencies.
More efficient than before : motion detectors of earlier times had problems in differentiating between the types of intrusions, that is, they failed to differentiate humans from dogs, cats and other animals, which affected their efficiency. But today, with the use of PIR or the passive infrared sensors, they can sense the nature of the intruding object more accurately. For instance, humans generally radiate infrared energy of 9-10 micrometers. Hence, the sensors are calibrated to sense between the range of 8 -12 micrometers. Also, the system is designed in such a way that it senses when there is a rapid change in the amount of infrared energy it is exposed to. For example, a walking person is easily detected and not a person who is standing still.
Also as the type of energy used by the motion detectors is light, the field of view of the device is wide according to the lens used to cover the sensor. The incoming infrared radiations can be focused and bent using plastic lenses. In some motion detectors, the provision of automatic adjustments for timing, amplitude and heat signatures are provided which help reduce the number of false alarms due to small targets like rats, rodents and pets, at the same not compromising the efficacy of the device in catching objects of the size of humans. Also different coverage patterns are also available to suit for large rooms, hallways or pet coverage.
Dual technology detectors combine the passive infrared signals and the active microwave signals to reduce the occurrence of false alarms. The active microwave transmits a signal of 10 GHz frequency that get bounced when struck on fixed objects inside the room which gives rise to a repetitive reflection that is sensitive to the difference in the nature of the background.
Limitations of PIR technology: though they can be a powerful tool in your home security system, there are certain limitations with wireless motion detectors. One among them is that unless the sensor is positioned properly, the device may see too much or too little. For example you may not want the system to go at every little event that take place. Therefore you have to take extra care while selecting the position of the device.
Another shortcoming with most of the PIRs is that they may not detect a body that is moving directly towards the sensor until it is really close to the device.
Another major limitation of the PIR sensors is that as they depend on the temperature of the body and the subsequent infrared radiation, if the wall of the room that is exposed to sunlight becomes sufficiently hot, then the sensor may not be able to detect the presence of human walking in front of it.
Installing wireless motion detectors: the installation process of the motion detectors is quite simple, though the positions where they need to be placed should be decided with a little bit of care so as to maximize the efficiency of the device. Once you have decided on the positions, you may follow the following procedure.
Choosing the right sensor: To make sure that you get the product that suits your needs, from the lot that is available, it is worth considering the following facts.
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