ABUS is known to me as a trusted brand for everything related to safety in and around the house, so I decided just for the smoke detectors from ABUS. Two pieces I bought, but one has already started to beep one day after commissioning. And neither as an indication for battery replacements even as a warning signal for smoke emission. Even after replacement of the battery, it beeped on - so the unit appears defective, the complaint is gone out, and I am still waiting for feedback. Pretty disappointing record, a defective of two ...