Driveway and garage monitors represent a class of home security that includes devices that serve various functions. The commonality among them is that they monitor activity in access areas to homes, such as driveways or garages. Some alert homeowners when they leave garage doors or driveway gates open. Many homeowners who may be prone to absent-minded behavior or those caught in emergency situations find them useful tools as the devices remind them that they need to close access to their homes. Others alert homeowners when individuals or vehicles enter their detection areas. Both kinds alert homeowners with a signal. Most conventional systems use a chime or alarm, however, the hearing-impaired may use systems adapted to activate light fixtures. Companies also offer systems which may monitor other areas of concern like pools. In general, they represent an affordable option to more elaborate systems with two-way communications systems.
These monitoring systems may utilize one of three sensor technologies.
Photoelectric/photo eyes emit an infrared (also known as infra-red) beam of infrared light. When an object breaks the beam, a signal is reflected back to the sensor's detection unit. A typical effective length for the beam may range from thirty to seventy-five feet. If objects do not break the path of the beam then the unit is not activated. Depending on your budget, you may want to choose a monitor with a photoelectric unit unaffected by rain, dust, and other weather-related occurrences.
Some other systems apply passive infrared radiation (PIR) technology. With their body heat, human beings radiate infrared energy, a wavelength that is found outside of the visible spectrum and contains very little energy. The energy pattern changes when human beings begin to move. Passive infrared (pyroelectric) sensors detect changes in this energy radiating between 8 and 12 micrometers, based on the heat radiated by human skin temperature. When the infrared light comes in contact with a temperature change the sensor activates the system, sending out an amplified signal to the alarm unit.
Another sensor operates on the principle of electromagnetic induction. That is, the detection systems conduct electrical current which changes according to changes in the surrounding magnetic field. Since metal causes a flux in the magnetic field, a corresponding change occurs in the electrical current that is reflected back to the detector. In access control, an electromagnetic field monitors activity and is activated when a metal object breaks the field.
Some devices work best when mounted in view of the driveway others are more suitable for ground level. A system may detect objects within a range covering dozens of linear feet either or hundreds of square feet. Systems may send an alert signal to a receiver located as much as two miles away.
Using this information, you should choose a system which best fits your individual needs. The most sensitive system is not necessarily the most appropriate. Also, many systems utilize wireless connections between sensors and alarm units. However, consumers should note that metal siding or roofs may interfere with this signal or reduce its range.