Here is the wiring. Didn't work in the first post. It is all powered by two AA batteries.

@Yveaux @gohan
I updated the library to 2.2 and I put a 47uf cap between ground and vcc of the pir (hope that's what you mean't) and now it works.

Thanks for your help!

I soldered now everything onto a pcb and now the pir doesn't work. I feel like giving up, didn't think that it would be that hard for me to build one stable node. I spent almost 2 hours soldering and assembling and now it doesn't work

@Yveaux
Sorry I have been a long time away due to exams.
Now I finally have time to spend for mysensors

I tried your approach with the three batteries. My setup looks like this:

I modified the HC-SR501 as shown below:

The sketch is pretty simple, it sends the motion and the light level and then goes to sleep with interrupt for 30 minutes. I still get the false positives whenever the arduino doesn't wake up from intrerrupt.

What am I doing wrong?

@mfalkvidd
And how can i tape the wire on the side of the battery holder? My battery holder package already has two wires connected like in the fritzing pictures.

@mfalkvidd
Awesome! How do i connect the wires to the battery? Solder them or what?

@Yveaux
That sounds like exactly what I want

Would it be possible to add a dht22 or would this interfere with the pir?

@Yveaux
Thank you very much.
I'll order a battery pack for 3 batteries, currently I have only a pack for 2 batteries.

How long does it take approximately till the batteries are empty? I know that it depends on how frequent the sensor gets triggered, but maybe you can tell me some average values.

@Yveaux
I found your other post here in the forum regarding the 3AAA batteries. Could you please explain how I do this?
Do I need to buy a battery pack for 3 batteries or is it possible do modify the battery pack I already have?
Sorry for bothering you with this type of questions, I just recently started with this.

@Yveaux
So i would need 5 batteries in total??
Seems like overkill to me, and the sensor would become quite big

@Yveaux
So what would you suggest? Adding a third AA-battery?
I just can't understand why some people got this pir sensor working on 2 AA batteries and without false triggers.

@Yveaux
Could you please explain why this will not work?
Because the pir sensor detects motion perfectly fine, the only problem are the false triggers, which occur when the radio sends the signal to the gateway.
I also saw some guys that run the exact same pir and arduino pro mini 3.3V version on 2xAA batteries.