To let you know.
I bought 2 very cheap pir sensors on ebay (10 euro for 2) and I tried them on my FHEM installation. They are recognized and seem to work!
Unfortunately they didn't send me any info about the dip switches so I have to scan the internet for more info about these sensors.
{HT}
Additional info:
You need a sensor which can be set on 3,3 Mhz. Not all sensors do this. In my sensor the used encoder chip is sc2262.
The usability of the sensor is limited as it is not very sensitive.
{HT}