“The currents these things run is down in the micro-amps now, and we run all the circuits from those micro-amp currents,” said Addy.
Overcoming wireless interference and security concerns
One of the common questions about wireless is reliability. A security system owner wants the peace of mind to know that if an intruder breaks into their home, the PIR mounted in the corner of their living room will properly detect the intruder and properly report that detection to the panel which can subsequently be reported to the alarm monitoring station for police response. That concern of reliability brings up the question of interference – especially as today’s homes feature more and more electronic and wireless RF emitting devices like microwave ovens, cordless telephones, wireless Internet routers and cell phones.
Fortunately for the security alarm industry, the wireless security devices are governed quite closely in terms of the frequencies they may use. According to Addy, the devices transmit wirelessly in lower UHF frequencies.
These wireless security and sensing devices from Addy’s business unit at Honeywell fall under FCC part 15 approval. It is a shared band licensed by the government for low-power devices like these sensors, keypads and wireless alarm fobs. The primary user of their frequencies – around 345 Mhz – is typically a government or military agency, and then commercial companies are the second, share user on this frequency band.
“It (FCC Part 15) limits the amount of power and on-air time that a certain device can have,” said Addy. “Its specifications reduce mutual interference between bands.”
Being very clearly specified in terms of power and on-air time (basically, the amount of time a device can be broadcasting a signal) reduces interference and this frequency usages separates these wireless security devices from other popular frequency bands like the 900 Mhz band (often used for cordless telephones) and the 2.4 Ghz band which is often used for wireless routers and susceptible to emissions from microwave ovens.
In terms of reliability, security is another strong concern. These wireless devices use device matching such that the receiving devices has to recognize the correct serial number from the signal-emitting device. Those are set into the receiver during the installation process, and then are checked whenever a signal is sent from the device using a cyclical redundancy check (CRC) – a simple circuit process that encodes or decodes and checks the data to ensure there is no interference and that the signal is not being spoofed from another device with a different serial number. In addition to the CRC, Addy noted that there have been increases in the technology which allow for many, many more unique device ID numbers than in the past.
“If you went back 20 years, they [the device ID numbers] were done with bit switches in the devices, so maybe you had only 64 or 128 device numbers. It was possible then that you could have two devices reporting the same number.”
Today such devices would be using an application specific integrated circuit (ASIC), which have grown more and more complex, thus eliminating the possibility of two devices appearing to a receiver as the same device. Today there are millions of combinations thanks to advances in these ASICs.
Where to use wireless
Technology advances aside, security system dealers have been finding more and more ways to use these wireless devices. Addy noted that an area of very promising growth for wireless is in outdoor sensors like motion sensors at a driveway entrance, where it would be virtually impossible to place wired devices due to the costs associated with powering the devices and running communication cables back to the central location.
The growth for wireless systems will also come in retrofit applications, where snaking wiring through existing, insulated and sheet-rocked walls is a chore. Historical applications are also a growth area, said Addy, since alarm dealers may not have permission or even wish to bore into a historical structure to install a security system.nOwners of older homes and buildings may also elect to use wireless to avoid ripping into walls which could have asbestos materials in them.