Z-Wave
Z-Wave is a sub-GHz mesh protocol (908.4 MHz in North America, 868.4 MHz in Europe) governed by the Z-Wave Alliance, known for strict certification, strong cross-brand interoperability, and zero Wi-Fi interference. Devices pair to a Z-Wave controller (SmartThings, Hubitat, Home Assistant with a USB stick, Homey), and it is the incumbent standard for locks, security sensors, and professionally installed systems.
The sub-GHz band is Z-Wave’s defining trait: it penetrates walls better than 2.4 GHz and never contends with Wi-Fi, Bluetooth, Zigbee, or Thread, at the cost of lower bandwidth and region-specific frequencies (a US device will not join an EU network). Every certified device must pass Alliance interoperability testing and expose standard command classes, so cross-brand compatibility is more dependable than Zigbee’s — a certified device works with any certified controller, at least for its standard features.
The trade-offs are a smaller, pricier catalog and a slower release pace than the Zigbee/Matter world; our dataset tracks 2,311 Z-Wave devices via the open-source Z-Wave JS project, versus 5,405 for Zigbee. Classic Z-Wave meshes are limited to 232 nodes and four routing hops — figures the newer Z-Wave Long Range mode rewrites entirely (see that entry).