Which frequency is not used for wireless security systems?

• A. 2.9 GHz
• B. 2.4 GHz
• C. 5.8 GHz
• D. 900 MHz

Answer: (A)

Wireless security systems rely on low-power, widely available radio bands that don’t require a license. The bands most commonly used are around 900 MHz for longer-range sensor links, 2.4 GHz for a broad ecosystem of sensors and controllers, and 5.8 GHz for certain video links and higher-throughput devices. The 2.9 GHz region isn’t part of the standard unlicensed bands used by home security equipment, and in many places it falls under licensed or restricted allocations. That makes devices built for 2.9 GHz rare and less practical, so it isn’t used for typical wireless security systems.