Does the owner press the doorbell of the residential security door for free or the property answers the indoor phone for free?

Generally installed by the construction unit. If there is nothing in the design, additional installation may be proposed to the construction unit or the owners' committee, and the installation cost shall be shared or paid according to the contract. Property companies are unlikely to invest in the installation. Even if the contract does not stipulate that the installation shall be carried out by the construction unit, it is up to the owners' committee to decide whether to use the maintenance funds or share them with all the owners. Property companies are specific operating and installing units. Of course, the installation requirements of a single owner are another matter, depending on whether they are available at the time of delivery.