Smoke detector beeping repeatedly irregularly

I have 9 pieces ABUS RM10 bought VdS smoke detectors in late July, 2013, as these were also evaluated by Stiftung Warentest as "good and cheap" (1/2013) (Rating: 2.2 as the best in the group "Smoke Detector with Alkaline Batteries" ).
It did not take long started the first a few times spread over the day and night to beep - first in the living room, now also in the bedrooms. Already at 4 pieces battery changed - no improvement. After all the reviews here, I suppose that this is a product defect. I will now return all 9. Based on my experience, I can only advise against any of this product.