I have tried a few cheap ready made 433MHz PIR sensors bought from eBay and aliexpress, but non of them worked with my Tellstick Duo/Nexa system. I decided to make my own, and here's the result. I'm testing the prototype now, using my own API to get push notifications on my Android phone when movement is detected in my office at home. Works like a charm.
Since this should work on 3V (for several months) I had use interrupts to make this happen. The Arduino will stay asleep as long as no movement is detected and only use about 0.3 mA. Using 2 1.5V AAA batteries (2700 mAh) will make this work for about 7.5 months on standby. I can live with that.
The circuit is pretty straight forward. One Arduino Pro Mini (3.3V), one cheap 433MHz RF transmitter (MX-05V) and one cheap PIR sensor (HC-SR501). All bought at eBay. The PIR sensor is actually for 5V, but I needed it to run on 3V. I found a hack to make this happen. If you decide to do this, make sure you get the right type of sensor. Some of them lack the extra pin out to bypass the 5V regulator. Search for HC-SR501 on eBay and you will find it.
The 433MHz transmitter works well. I have my Tellstick Duo in the basement, and the transmitter works well trough at least one floor. I will test range later, as I plan to put one in the shed later. I might have to move the voltage up to 9V to increase the range.
I plan to build a few of these and have around my home. I will post the PCB layout when they are finished. Stay tuned.