My recommendations for the best RF motion sensors on 433 or 315MHz frequency. These devices are very decent quality and only cost $15AUD. They feature battery and micro-USB charging, a motion indicator light and emit a strong signal.
One subsystem in my home automation setup is a RF receiver module that reads in signals and converts them to messages sent to Home Assistant. You can view my previous post about the best wall panels compatible with this system.
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Best Motion Sensors
KERUI Motion sensor (battery or Micro USB powered)
This is one of maybe 4 different motion sensor models I have tested. The KERUI costs about AU$12-15 and is very reliable.
I run two with a Micro USB cable attached. The others run on 3 AAA batteries (have not had to change any batteries in 3 years, meaning they use very little energy).
Highly recommended because they detect motion reliably, and send out a strong signal that can be detected all around the house.I have had no problems with this model and it happens to be a good-looking and functional design as well. (Some designs look very cheap or have round bottoms making it impossible to just place on a shelf without mounting it properly.)
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The front features a LED to indicate when motion is detected. There is an on/off switch on the side and a Micro USB port for powering. The back has a battery compartment. Mounting options via ball joint are provided in the box.
I purchased mine on KERUI Official Store on AliExpress (affiliate) where they are sold for around AU$13.
Another Kerui product I tried is a different motion sensor model (affiliate) which I can recommend as well. It appears to have a wider detection area, though I doubt there is much difference.
Conclusion
I want to create a list of affordable hardware that people can use to create budget home automation systems. Let me know in the comments which motion sensors you have tried that work well with your system. Also, check out my previous post for more hardware recommendations.