Alarm and security is a broad term that includes applications such as access control, smoke alarms, social alarms, and intruder alarms. One of the key drivers in this segment is intruder alarms.
A deciding factor for buying an alarm system is typically an increased feeling of safety; hence the market growth does not necessarily follow consumer markets like the more convenience-oriented home automation segment, keeping growth rates even in economic downturns.
Legacy intruder alarm systems were based on wired sensors. The need to draw wires from the alarm panel to all doors and windows drives up installation cost and also represents a barrier for end customers not accepting wires around the house. The availability of low-cost, high-performance integrated RF devices paved the way for RF-enabled sensors. Using wireless sensors dramatically speeds up installation time, and also enables DIY installation, both of which significantly drive down system cost. The return on investment for designing an RF-enabled security system therefore justifies the addition of RF devices in all the nodes. Intruder alarm systems migrating from wired to wireless, with typically five to 10 sensors per installation, is therefore an important driver for the low-power RF market.
Low-power operation is important for an alarm system. Sensors are battery-driven, and there is a limit on how often the end user wants to change batteries. A typical requirement is three to five years of battery lifetime in the sensors. To get a long battery lifetime, sensors are duty cycled. The duty cycle sets the latency/response time for triggering the alarm, which is another key system parameter.
To have very low average current consumption (ĶA range), the RF device needs to be able to change from low-power state to active state quickly to minimize the time spent in high-current modes. Smart features in the RF transceiver can also dramatically reduce the current consumption, such as an RX sniff mode in some TI devices, which automatically duty cycle the radio to achieve less than 3 mA current consumption during the protocol listening period.
With the availability of low-power, low-cost integrated devices, in combination with a strong market demand to avoid wire clutter, the number of RF-based alarm installations is rapidly growing. Looking at the market today and five to 10 years into the future, one will see that the problem of interference will dramatically increase.
When designing an alarm system, strong co-existence properties are critical to handle interference from other wireless devices, and also from intentional interference/jamming. A problem of interference will result in reduced range or loss of communication. Choosing an RF device with good co-existence properties is critical to ensure first-pass installation success and problem-free operations also in the years to come. The co-existence properties are defined by the RF device selectivity and blocking performance.
Figure 1: Best case scenario of alarm systems with no interference so both connect to all sensors.
Let's look at what co-existence means in an everyday environment, using a typical alarm system as an example (See figure 1). To the left is a system with good co-existence properties (TI's Sub-1GHz performance line), to the right you see a system based on a device with weaker co-existence properties. The green dots represent the alarm panel/alarm central and the yellow dots represent the alarm sensors (window sensors, motion detectors etc.). The blue area represents the range for the system, showing coverage for all sensors for both systems.
Let's look at what happens if an interferer device enters the environment. In this example, let's assume a wireless headset (See figure 2).
Figure 2 : Typical example of alarm systems with interference showing the importance of co-existence properties in regards to performance, with TIís sub-1 GHz performance line (right).
To the right, the wireless headset interferes with the range of the alarm panel, making it impossible to communicate with the further out sensors. Since the alarm panel range is reduced, the alarm system installation fails. If this is temporary interference, the system will experience unreliable communication with the sensors, which is unacceptable for a safety critical application like an intruder alarm.
To the left is the same example using a system based on the TI Sub-1GHz RF performance line. The wireless headset enters the environment, but the range of the alarm panel is not affected. This translates to longer range, ease of installation, and robust and reliable communication.