Heat from transformers
A broadband modem and cordless telephones, halogen lamps and mobile telephone chargers all have transformers which connect the mains socket.
The transformer converts the voltage which comes out of the mains socket to the voltage the apparatus is built for, for example 12 V (volt).
A transformer uses electricity even if the lamp is not lit or the mobile telephone is not connected to the charger. Feel the transformer yourself. It is warm when it is connected to the power outlet. If it is warm, it is using electricity.
The picture below, taken with a heat camera, shows how warm a common transformer becomes. The light yellow surfaces in the picture show heat and the dark-blue surfaces are cold.
The transformers for a broadband modem and a mobile telephone are connected to an extension cable. The casing is light-yellow in the picture and has a temperature of around 60° Celsius.
In order to reduce the heat losses from the transformers you have at home, you can connect them to an extension socket with an on/off switch. It is then possible to switch off the apparatus completely when it is not being used.