What RF interference source operates in the same 2.4 GHz ISM band as Wi-Fi and is commonly found in consumer IoT deployments near wireless access points?

• A.Bluetooth devices (phones, speakers, headsets) use the 2.4 GHz ISM band (2.402-2.480 GHz) with frequency hopping spread spectrum (FHSS); while Bluetooth uses adaptive hopping that avoids occupied Wi-Fi channels, high density of Bluetooth devices can still degrade 2.4 GHz Wi-Fi performance
• B.ZigBee IoT devices exclusively use 915 MHz and do not interfere with 2.4 GHz Wi-Fi
• C.Baby monitors using the 5.8 GHz DECT standard interfere with 5 GHz Wi-Fi channels only
• D.Smart lighting systems using Z-Wave operate at 2.4 GHz and are the primary interference source in IoT environments; a wireless site survey is needed only outdoors; indoor propagation is uniform. Directional antennas radiate equally in all horizontal directions, unlike omnidirectional ones