Another route to go is Xiaomi motion sensors. They are tiny, respond near instantly to motion in HA, battery powered and cheap (under $10). You need the gateway though. But Xiaomi have plenty of other cheap, good quality items like door sensors, temp/humidity etc that are equally cheap.
The problem with Xiaomi motion sensor report the detection only every X seconds no? So their would be a delay that is ok for security, but not for automatic light for example.
If you build a 433MHz receiver you’ll be able to receive the signal from the different sensor (movement, door, water leak, …).
But you wont be able to know if the alarm is armed or not (except if the central send a signal when armed/unarmed, but I take that for unlikely).
No, for motion they are instant. I have 5 or 6 and they are great for motion. for lux that isn’t great as it only records every hour (i think) or when motion.
I have 1 at the top of the stairs and is used to turn the landing light up higher from dimmed when motion is detected. I don’t even get to put one foot on the bottom stair and motion is detected. Maybe 3-4m up the stairs.
i wasn’t wanting yet another hub, but these are really good and in my opinion.
Which sensor exactly is it? The XIAOMI Mi Human Body Sensor ?
Also why not consider a RTL-SDR receiver acting as a 433mhz receiver?
You can pick up these for less than $10 on ebay (they are basically DVB-T receivers with modified driver/firmware).
You can deploy a docker container that does rtl_433 to mqtt bridge.
I have a 433mhz power monitor that I have in my project list to support like this.
Of course RTL-SDR is receive only, so this is a one way bridge.
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yes that is the older one without the light sensor
newer version is
Original Xiaomi Smart Home Aqara Human Body Sensor
which comes with a stand, ceiling/wall mount
i have both and both detect the same.
Mine too, pretty much instant. They are by far the most cost effective solution I have found.
For what I have read in this post I think this is the most cost effective solution. Does these sensores connect directly to the local wifi network? or do you need a brick like the Philips Hue?
You need the Xiaomi Gateway or you build/use something like this: Zigbee2mqtt: getting rid of your proprietary Zigbee bridges (Xiaomi, Hue, TRADFRI)
For what it’s worth… I went Aeotec Z-Stick Gen5 and Neo CoolCam Battery Powered PIR Sensor (along with Neo CoolCam Door/Window Detector sensors) - For the price point, it was worth it. Was fortunate that I was able to buy 3 of each on Amazon as a pack for around $50/pack and around $50 for the Z-Stick - cordless drill, some swearing, some posting here and up and running they were and still are. Works like a charm. They don’t detect temperature but do handle light/motion. The door/window sensor is just that (simple reed switch.)
Probably a little too sensitive I suppose as my wife got tired of notifications of motion in the house when we’re away at work and the dog decides to go on a walkabout - but I can’t complain for ~$150 into it.
@MarkR , @eiolos thank you guys for all the details.
I’m choosing sensor for my smart home and wonder how long does the battery last for Xiaomi Smart Home Aqara Human Body Sensor ?
I’ve had mine for about 9 months so far and not replaced any batteries yet (they were not at 100% when I got them). They are all somewhere in the range 43% to 52%, so probably good for another 6 to 9 months depending on foot traffic.
@touliloup
I know it has been a while but are you still happy with these Kerui P829 sensors?
I have some motion sensors (which I use in conjunction with a Sonoff RF Bridge) and they have been driving me mad! The documentation says they sleep for 3 minutes after 4 activations within 3 minutes which is fine but it what it doesn’t say is that they carry on detecting motion during that 3 minutes sleep period but don’t send a signal! This means I cannot know when they will wake up so can’t set any controls in HA based on motion.
Do these sensors simply send a single signal every five seconds or every 5 minutes with no fancy sleeping?
Thanks.
These don’t go to sleep and simply send a signal as soon as a movement is detected.
I would suggest getting a conbee stick to talk to the Xiaomi zigbee stuff… This can plug directly into your HA (wherever that may be) and you can control network etc via deconz… It is way less fiddly than setting up zigbee to mqtt…
but is it ZigBee or Z-wave is i do not want to add zwave?
I see the Xiaomi Aqara Zigbee motion sensors mentioned a lot recently. Conbee is Zigbee. or there are cheaper Conbee alternatives https://www.zigbee2mqtt.io/information/supported_adapters.html
Are they zwave or zigbee? i think zwave and they are not pet immune?
I said Zigbee in the message 
They are 100% Zigbee. Definitely not ZWave.
Not sure about pets I’m afraid, though have seen some posts where people have said they angle PIRs or put tape over the lower half of the sensor to avoid picking up the animals.