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. Smile
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 (See the links for more information)
Arduino Pro Mini 3.3V
433MHz RF transmitter (MX-05V)
A cheap transmitter found on eBay
PIR sensor (HC-SR501)
A cheap sensor found on eBay. Make sure to get the right one if you want to run on 3V