Why Wi-Fi Is Not Wireless for Alarm Systems
Wireless makes installing alarms easy, not just because wireless sensors use radio frequency (RF) to communicate, but because they really have no wires. Wireless alarm sensors are battery-powered and can be installed anywhere because they are truly wireless.
However, the term wireless has more than one definition. Wireless IP cameras are different because, while they transmit over Wi-Fi, they are not battery-powered — they still need a power cable to operate (at least not for more than a few hours). Having a power cord fundamentally changes the installation, different from the “lick and stick” of traditional wireless alarm devices.
There are other differences as well. All wireless alarm systems use much lower RF frequencies (400MHz-900MHz) to communicate to peripheral devices than the 2.4GHz used in Wi-Fi. The lower frequencies penetrate building materials better, going through walls, ceilings, floors, furniture and office cubes. This is the same reason that police radios use the 700MHz-900MHz frequency band; they are still able to communicate indoors when they move through a building or campus.
The high 2.4GHz frequency of Wi-Fi is not designed to penetrate building materials but does transmit large amounts of data. Instead, Wi-Fi is designed to bounce off walls and other surfaces to maximize coverage. This is why “dead spots” occur in home and office Wi-Fi networks. There is also the issue of power consumption.
The lower frequencies used by alarm systems also provide better range for the same power, important for a battery-powered device that needs to run for years on a couple of AA batteries. While we may not think about it, we see these issues reflected in the marketplace. We do not find Wi-Fi door contacts or PIRs in the product catalogs because they need a power cord and don’t fit the wireless alarm model.
Wireless alarm systems are built around the battery-powered paradigm to maximize easy install. The ability to penetrate walls, floors and other building materials is crucial for the alarm installer because it helps eliminate “dead spots” and frustrations with limited range.
As video verification becomes mainstream, the difference between battery-powered and Wi-Fi power cords becomes significant. The new wireless battery-powered video cameras build upon the wireless alarm model while the power cords on Wi-Fi cameras don’t. The battery-powered sensor/camera is still fundamentally an alarm device. While both wireless products can provide video verification, Wi-Fi still has wires and is not really part of the alarm system or installed like an alarm device.
Again, we see this reflected in the marketplace as most surveillance cameras are not wireless. Once there is a need for a power cable, running an additional Cat-5 Ethernet cable makes sense and is the typical installation. IP cameras certainly deliver great value, but they don’t follow the wireless lick-and-stick installation model that made wireless alarm systems so popular.
While perhaps not enough for megapixel images, the 900MHz bandwidth is broad enough to do full VGA video and more than sufficient for video verification — the driving force to add cameras to wireless alarms in the first place.
Keith Jentoft is President of RSI Video Technologies, based in St. Paul, Minn. He can be contacted at [email protected].
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