Sonoff SNZB-04 Review: A Cheap Zigbee Contact Sensor That Works, Until It Drops Offline
An affordable Zigbee door/window sensor that pairs easily with SmartThings, Home Assistant and Hubitat, but a flimsy case, a loose battery holder and periodic disconnects hold it back.
The Sonoff SNZB-04 is a budget Zigbee door and window contact sensor that appeals mainly on price and easy pairing. It connects directly to Zigbee hubs, SmartThings, Home Assistant (ZHA), Hubitat, and even an Echo with a built-in Zigbee radio, often in seconds without any Sonoff app, and for some owners it's the only sensor that paired cleanly after they tried others. When working, it's reliable with no false positives and decent battery life. But its 3.7-star average reflects two recurring problems. First, disconnects: a number of owners find that after a few months it drops offline once or several times a week, or shows 'unavailable' in Home Assistant or Alexa and needs deleting and re-pairing, which is exactly when you don't want it (for example, while you're away). Second, hardware: the case feels flimsy and is awkward to open, and the loose battery holder often won't maintain contact without bending it or shimming the cell, on a frequently-used door the battery can even dislodge. The included mystery-brand battery is unreliable too, so owners recommend swapping in a name-brand cell (and note it sometimes ships without one despite the listing). Pairing also needs the sensor close to the coordinator. For a cheap sensor on a well-built Zigbee mesh, it can be fine, but for set-and-forget reliability, several owners moved to Aqara instead.
- Budget Zigbee door/window sensing
- SmartThings, Home Assistant or Hubitat users
- Non-critical monitoring
- Simple automations and routines
Pros
- Cheap and affordable
- Easy, direct pairing with SmartThings, Home Assistant (ZHA) and Hubitat
- Reliable open/close detection with no false positives when connected
- Works with Google Home, Alexa and IFTTT for routines
- Can pair to some Echo devices without a Sonoff hub
Cons
- Drops offline / shows 'unavailable' after months, needing re-pairing
- Flimsy case and a loose battery holder that often needs shimming
- Unreliable included battery (sometimes not included at all)
- Pairing needs the sensor close to the coordinator
- No Apple HomeKit or Matter
Who is the Sonoff SNZB-04 for?
This is an affordable Zigbee door and window contact sensor that requires a Zigbee hub (a Sonoff Zigbee Bridge or a third-party coordinator). It works with SmartThings, Home Assistant (ZHA), Hubitat, and integrates with Google Home, Alexa and IFTTT, but not Apple HomeKit or Matter. It runs on a CR2032 battery. It best suits budget-minded buyers who want cheap Zigbee sensors, SmartThings/Home Assistant/Hubitat users, and non-critical monitoring or simple automations. Given the reliability and build caveats, it's less suited to security-critical use where a dropped sensor could matter, if you need rock-solid dependability, read the caveats first.
What buyers love
Value and easy pairing are the draws. It's inexpensive, and it pairs directly with Zigbee hubs, owners report connecting it to SmartThings without any Sonoff software, adding it to Home Assistant via ZHA (a ConBee II coordinator) in about two seconds, and integrating cleanly with Hubitat, and some even pair it to a 4th-gen Echo with a built-in Zigbee radio to trigger routines with no Sonoff hub at all. For several buyers it was the only sensor that worked after others demanded proprietary apps and still wouldn't connect. When it's running, owners are happy: reliable open/close detection, no false positives, good battery life on some units, and easy scenes and routines via Google, Alexa or IFTTT. For a low-cost sensor to add door and window awareness to an existing Zigbee network, it can do exactly what's needed.
What to know before you buy
Two issues recur. First, reliability: while some units run for months at 100% battery, a notable share of owners find the sensor dropping offline after three to six months, once or several times a week, or showing 'unavailable' in Home Assistant or Alexa until it's deleted and re-paired, which can leave you without coverage exactly when you want it (for instance, while away on holiday). Second, build quality: the case feels flimsy and is difficult to open, and the loose battery holder frequently won't maintain contact without bending it or wedging something between the battery and case, on a heavily-used door the battery can dislodge entirely. The included battery is a mystery brand that owners find unreliable, so the common advice is to replace it with a name-brand cell immediately (and note it sometimes ships without a battery despite the listing saying otherwise). Pairing also needs the sensor placed close to the coordinator, and the kit is stingy on adhesive strips for the price. Owners frustrated by the disconnects and build often switch to Aqara sensors, which they find more stable on ZHA. There's no Apple HomeKit or Matter support.
Is the Sonoff SNZB-04 worth it?
For a cheap, easy-to-pair Zigbee contact sensor on a solid Zigbee mesh, the Sonoff SNZB-04 can be worth it, it's inexpensive, works with SmartThings, Home Assistant, Hubitat, Google, Alexa and IFTTT, and performs well when connected. The catches are real, though: periodic disconnects that require re-pairing (a problem for anything security-critical), a flimsy case, and especially a loose battery holder that many owners must shim, plus an unreliable included battery. Buy it if you want a budget sensor for non-critical monitoring and don't mind swapping in a name-brand battery and occasionally re-pairing; if you want set-and-forget reliability or better build, many owners point to Aqara or another sensor instead.
Frequently asked questions
Does it need a hub?
Yes. It's a Zigbee sensor that requires a Zigbee hub, a Sonoff Zigbee Bridge or a third-party coordinator. It pairs easily with SmartThings, Home Assistant (ZHA) and Hubitat, and integrates with Google Home, Alexa and IFTTT. Some owners also pair it to an Echo with a built-in Zigbee radio. There's no HomeKit or Matter support.
Why does it keep going offline?
It's a common complaint. After a few months, some units drop offline once or several times a week, or show as 'unavailable' in Home Assistant or Alexa and need to be deleted and re-paired. A loose battery-holder contact contributes, so shimming the battery helps, but the disconnects make it less ideal for security-critical use.
Should I replace the included battery?
Yes. The included mystery-brand CR2032 is unreliable, and swapping in a name-brand cell (like an Energizer) resolves erratic behavior for many owners. Note that despite the listing, it sometimes ships without a battery at all, so have a spare CR2032 on hand.
Why won't it pair?
Two things help. Pair it close to your Zigbee coordinator (it needs to be within whispering distance to join reliably), and if the battery contact is poor, bend the holder or shim the cell so it makes solid contact. Once joined at close range, you can then mount it in its final location.
How's the build quality?
It's the weak point. The case feels flimsy and is awkward to open, the circuit board can sit loosely, and the battery holder often won't maintain contact without adjustment, on a frequently-used door the battery can even dislodge. For sturdier, more reliable sensors, owners often recommend Aqara instead.
