The tenants lodged an appeal against this and the BGH ruled in favor of the tenants. The BGH found that the replacement of the smoke detectors did not meet the requirements for a rent-increasing modernization measure, as they were equivalent devices and therefore did not constitute a technical improvement. The BGH also pointed out that the mere fact that the landlord now installed its own devices instead of the previously rented ones made no difference.
This ruling is an important reminder for landlords and tenants. Modernization measures that can lead to a rent increase should offer added value and represent an improvement on the status quo. Simply replacing old appliances with new, equivalent appliances does not necessarily justify a rent increase.