Zigbee
Low-power mesh radio for IoT — smart bulbs, sensors, locks. Built on IEEE 802.15.4.
Standardised in 2003. Mesh: every router node forwards traffic, so range scales with device count. ~250 kbps, ~10–100 m. Philips Hue, Ikea Tradfri, Aqara, many smart locks. Competitors: Z-Wave, Thread, Matter (Matter rides on Thread or Wi-Fi). Hubs (Hue Bridge, Aqara M2) translate Zigbee into IP. The Connectivity Standards Alliance (CSA) owns the spec.