Sensors are installed in about 20–30% of all the apartments in the building, one per apartment. Basically, the sensors are installed in the corner apartments on the top and bottom floors of the building or in apartments that are deemed to be constantly cooler or warmer. The sensors are installed on the wall at a height of about 1.1–1.5 meters from the floor. The apartment sensors measure the temperature and humidity of the apartments. The residents themselves can have a say with regard to the location of the sensors, but they should be installed in a place where draught or heat from a radiator or other similar issues have no impact on the sensor reading. The sensors are normally attached onto the wall with two-sided tape. If tape attachment is not suitable, it is possible to use other attachment methods as agreed. The sensors are battery-powered, and their measurement data can be monitored via a cloud service. The data transmission of the sensor operates with the modem and data connection located in the heat distribution centre. With the sensors, the operation of the heat distribution centre can be controlled also according to the indoor temperature in addition to the outdoor temperature. That way, indoor temperature can be taken into account better in the heating controls and the residents have more pleasant indoor conditions.