Third Reality Zigbee motion sensor review: cheap, quiet, and good at its one job
Disclosure: Third Reality didn’t send me these and doesn’t know this review exists. There are no affiliate links in this post. How I review
Short version: I run four of these, and I like them. They’re cheap, they’re running in Home Assistant over ZHA, and the one in my busiest room has logged about 2,300 state changes in the last week while barely denting its battery. The catch, which probably isn’t theirs: three of my four are currently offline, and I’m fairly sure my Zigbee network is to blame, not the sensors.
What it is
A small battery-powered Zigbee motion sensor. Two AAA batteries, rated for about two years of typical use. Detects motion up to 20 feet. Marketed as pet friendly. Supports over-the-air firmware updates. It needs a Zigbee hub, and Home Assistant is on Third Reality’s own compatibility list. Third Reality lists it at $19.99, with a sale price of $14.99 and multi-packs available. In Home Assistant (ZHA) it shows up as model 3RMS16BZ.
How I use them
Four sensors: living room, office, laundry room, bedroom. The main job is night lighting. After 10:30 PM, motion in the living room, office or laundry room brings the lights up to 20% so nobody’s blinded at 2 AM, and they shut off again when the room goes quiet. The bedroom one handles daytime motion lighting.
It’s a simple job, and it’s exactly the kind of thing a $15 sensor should do well.
What works
- Paired through ZHA, each one exposes motion, battery, signal strength, firmware and a detection-interval setting in Home Assistant.
- The living room sensor is the workhorse: about 2,300 state changes in the last seven days, and its battery has gone from about 90% to about 82% over the last three months. If that rate holds, it’s on track for the two years Third Reality claims, or better.
- It’s small and inoffensive. It sits there and does its job.
What doesn’t
Three of my four are offline right now.
- The laundry room and office sensors haven’t reported anything in months.
- The bedroom sensor worked until October 20. In the two months before that, its battery dropped from 97% to about 50%, a lot faster than the living room one.
Before blaming the sensors: I audited my Zigbee network and it has no routers. Every device on it is battery-powered and has to reach the SONOFF ZBDongle-P coordinator directly. The living room sensor has the healthiest link to the coordinator, and the others are the ones that dropped. A sensor with a weak connection also tends to burn battery retrying, which would explain the bedroom drain. It’s also possible the laundry and office units simply ran their batteries down; I have no battery readings from either since early August. I can’t prove the mesh is the whole story yet. I’m adding routers and will update this review with whether the three come back.
Who should buy it
Buy it if you want cheap, simple motion triggers for lights in Home Assistant and you have a healthy Zigbee mesh, meaning at least a few mains-powered devices like smart plugs acting as routers.
Skip it, or plan around it, if your network is all battery sensors like mine, or if you need presence that holds while someone sits still. A basic motion sensor sees movement, not people.
Verdict
I like these. For the price they do their one job well, and the one with a good connection has been steady and easy on batteries. My dead ones probably say more about my network than about Third Reality, and I’ll confirm that in an update once the mesh is fixed.
My rating: 4 out of 5
Specs (from Third Reality’s product page)
| Price | $19.99 list, $14.99 sale (multi-packs available) |
| Power | 2 × AAA, about 2 years claimed |
| Range | Up to 20 ft (6 m) |
| Compatibility | Zigbee hub required; Home Assistant listed |
| Updates | Over-the-air firmware |
| Model (as seen in HA) | 3RMS16BZ |
Source: thirdreality.com
