Multiple-Pipe Central Heating
This solution is ideal if you live in an apartment with central heat, individual heat meters, and a multiple-pipe heating system. To use, place a temperature sensor in each room with a radiator. This lets you control each room individually. When the temperature in a room drops below the desired settings, the heat will turn on. When the temperature is hotter than the pre-set settings, the heat for that room will turn off.
Note that this solution will work whether or not you have an individual heat meter. But you'll only save money on heating bills with a meter. These are the required parts for this solution: