Recently, I talked about this Tuya Zigbee presence sensor with a round shape, based on the S3KM111L mmWave radar. I’ve encountered this particular model in a total of two devices and they both turned out to be really solid, the second one being the MTG075-ZB-RL.
In this article, I am testing a new Tuya Zigbee 24GHz Presence Sensor based on the HLK-LD2410 mmWave radar. The LD2410 is well-known and already proven, used in devices like the Apollo MSR-2 and the Moes ZSS-LP-HP02. I have high expectations going into this review, so let’s see.
This device is white labelled as model SZR07U and is available on AliExpress for about $15.
Technical Specification
- Model: Tuya 24Ghz Presence Sensor SZR07U
- Connectivity: Zigbee 3.0
- Detection Angle: 120×120°
- Detection Distance: 6m
- Input: 5V1A USB-C
- Cable length: 45cm
- Dimensions: 60x60x15mm
- Price: $15.99 @ AliExpress
Teardown and Package Contents
The Tuya SZR07U Presence Sensor ships in a very low-quality box, containing the device itself, a USB-C cable, a sticker for installation and a user manual. As usual, the box came banged up but the device remained intact.
It has a simple square-ish shape with some lines printed on the front. I assume these are supposed to indicate the millimeter waves from the radar sensor, but are, of course, irrelevant. The backside of the device has a small hook hole that you can use to mount the sensor on a nail or screw. I suggest simply using the sticker, as the device is very light and can be mounted anywhere.
Opening up the Tuya SZR07U Presence Sensor took just a simple prying up of the backplate. The PCB is very simple and small, holding the sensor, communications module and USB-C connector.
Like I mentioned earlier, this model uses the Hi-Link HLK-LD2410 [Datasheet] mmWave radar. It relies on the Tuya ZTU [Datasheet] communication module. I’ve encountered this particular SoC in many devices, for example this Tuya 24GHz round presence sensor and the awesome 12-channel Zigbee relay board. I’ve never had issues with the performance of this module and I don’t expect it will different with this device.
Home Assistant Integration
The Tuya SZR07U Zigbee Presence Sensor is supported in Home Assistant through Zigbee2MQTT. To pair it, you need to hold the button for about 7 seconds until the device enters pairing mode and the indicator LED starts blinking.
Zigbee2MQTT
Once paired, the device is identified as model SZR07U by manufacturer Tuya. It’s unique Zigbee manufacturer identifier is set as _TZE204_muvkrjr5. It operates as a router in the Zigbee mesh network, capable of relaying traffic from adjacent devices back to the coordinator.
The entities exposed in Home Assistant through Zigbee2MQTT are rather simple. You can tweak the sensor’ detection range, radar sensitivity, fading time and toggle the indicator LED. There’s a target distance sensor that measures the distance in centimeters surprisingly accurate.
Heading over to the Logs section and unfortunately, my doubts got confirmed:
Just like the Moes/Linptech model, the Tuya SZR07U floods your Zigbee network HARD. It sends a payload every second, sometimes twice in a single second. This frequent update rate comes from the target distance sensor, which keeps changing even at the smallest movements.
Since Tuya devices are designed to PUSH and not POLL, you are unable to control the update frequency. It is possible to debounce the messages in Zigbee2MQTT, but that will only limit the entries added to the database. At the moment, this is a known but unfixable issue, as it can only be corrected with a firmware update from Tuya.
Okay, so what does it mean?
Well, if you have a stable and resilient Zigbee network, based on a good coordinator (e.g. SLZB-06), you will have no issues whatsoever. Deploying several of these sensors would not overload the network and things will function as normal.
If you have an older coordinator or have too many devices (100+), deploying two or more of these would most certainly cause lag, delays and possibly crash your network entirely. The real-world performance (and any potential issues) will depend on a lot of factors, I highly suggest you go over my detailed article for building a stable and robust Zigbee network to at least mitigate some of them.
Testing performance
With the network flood issue in mind, I went ahead and tested the actual performance of the Tuya SZR07U sensor. As this is not my first rodeo with a LD2410 mmWave radar (Moes, MSR-2, DIY Sensor), I installed it in a corner of my office and carefully monitored it’s performance. Here’s a summary in a few sentences:
The initial detection is as good as a PIR motion sensor, it immediately changes state as soon as I enter the room. The target distance sensor is also updated immediately, jumping up and down in value until you stop and stay still. Once I settle and don’t move, the sensor stabilizes and measures the target distance surprisingly accurately.
At a distance of 0 to 4 meters, the devices detects static presence perfectly. There are no false negative triggers and performance is very reliable. The parameters set in Zigbee2MQTT are respected by the sensor, which means the external converter is correct. Setting the fade time to 15 seconds correctly clears presence at 15 seconds, with a possible ±2 seconds difference.
At a distance of 4-5 meters, false negatives start to appear, especially when I’m laying down on my office sofa. Although it happened 1/5 times in my tests, it’s enough to acknowledge that this is where the sensor performance deteriorates.
At a distance above 5 meters, false negatives are more frequent and the performance becomes unreliable. In all fairness, this is the official specification of the LD2410 sensor: motion detection up to 8 meters and presence detection up to 5 meters.
Summary
The Tuya SZR07U Zigbee Presence Sensor delivered nothing more and nothing less then what I expected. The LD2410 performs as spec’d, with the same parameters as other devices carrying the same mmWave radar sensor.
Parameters set in Zigbee2MQTT are respected, allowing you to tweak the detection range and sensitivity to match your space. The presence clear timer is also on point, if that matters for your automations.
The communications module holds a robust link to my coordinator, with the LQI floating from 200-250 at a distance of about 4 meters. There is no reason to think the ZTU is going to be a bottle neck for this device, as it was not for many others I’ve tested with the same module.
Unfortunately, the Zigbee network Flood is potentially going to be a problem for some people. In my honest opinion, this issue is overblown, but it does largely depend on the health and overall stability of your Zigbee mesh network. Building, configuring and maintaining a proper Zigbee network requires time, patience and a lot of trial an error.
If you want to try out the Tuya SZR07U Presence Sensor for yourself, here’s a few links where you can get it. If you are looking for a better Zigbee alternative, I would suggest taking a look at the MTG075-ZB-RL (24GHz) or Sonoff SNZB-06P (5.8GHz). Or just get an Apollo MSR-2 and forget about any issues with presence sensors.
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