So, what could this mean?
De device should be supported by rfxcom and it does work standalone but it is not detected in the RFXmngr and therefor does not work in domoticz.

The fact the it works standalone means it is transmitting but the RFXcom is not registering?!?

I checked just now and no, it's not.

Hi, Reading this posting I decided to pick up one of these cheap chimes at Action. The one I have says 200689101 on the back of the chime. This is the exact same modelnr as stated in the RFXcom user guide in the supported protocols alphabetical list (2.2.2) SelectPlus200689101 & SelectPlus200689103 ...