Your apartment’s handset is part of a complex network. Incorrect wiring (reversed polarity) creates “noise” or a short circuit in the entire system. As a result, your neighbors may stop receiving calls, or the front door lock may fail. If a DIY installation causes a system-wide failure, the resident responsible will be liable for the repair costs and call-out fees. 

Advice:

Ensure compatibility before buying a handset, or better yet, let a professional handle the installation.

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