update:
Adapted the old distance sensor sketch to the 2.0 library and upladed it and connected to my PC. Also connected the gateway 2.0 to raspberry (Domoticz).....
Allright it works....I do get distance in my serial monitor and in domoticz.
Now try to upload the basement alarm sketch...See what happens...
To all,
Thanks for your answers. Unfortunatly I didn't have time to check your answers. I will keep in touch
Hi,
I promised to keep in touch.... 
I have disconnected the radio from the Arduino, so the radio is fed through a seperate stable 5V.
And also the relais board is fed seperately.
It runs for a cuple of days and it seems to work well. Time to move on.
To see if the magnet is working or not, I decided to connect a RGB led. When I connect the led, the board is going bonkers. The led is connected on D5 and D6 and the other side to ground (via a resistor)
Anybody a clue?
Again, thanks all for answering
Until now its working 2 days flawlessly.