Many hotels experience little or no mobile signal inside the building, even when they are located in big cities. Walls are usually of thick stone, or mass concrete. Windows are usually triple glazed, and the doors are increasingly fire doors with a layer of metal in them. All this prevents mobile signal from entering. Hotels are often located within one hundred metres of the operator’s tower but still experience poor signal inside. Customers and staff may have to stand beside the window to get a good signal. This is far from ideal.